Add xaringanthemer rmarkdown template

inst/rmarkdown/templates/xaringanthemer/skeleton/skeleton.Rmd

+---
+title: "Presentation Ninja"
+subtitle: "\u2694 <br/>with xaringan and xaringanthemer"  
+author: "Yihui Xie"
+date: '`r Sys.Date()`'
+output:
+  xaringan::moon_reader:
+    lib_dir: libs
+    css: xaringan-themer.css
+    nature:
+      highlightStyle: github
+      highlightLines: true
+      countIncrementalSlides: false
+---
+
+```{r setup, include=FALSE}
+options(htmltools.dir.version = FALSE)
+library(xaringanthemer)
+solarized_dark(
+  code_font_family = "Fira Code",
+  code_font_url    = "https://cdn.rawgit.com/tonsky/FiraCode/1.204/distr/fira_code.css"
+)
+```
+
+background-image: url(https://upload.wikimedia.org/wikipedia/commons/b/be/Sharingan_triple.svg)
+
+???
+
+Image credit: [Wikimedia Commons](https://commons.wikimedia.org/wiki/File:Sharingan_triple.svg)
+
+---
+class: center, middle
+
+# xaringan
+
+### /ʃæ.'riŋ.ɡæn/
+
+---
+class: inverse, center, middle
+
+# Get Started
+
+---
+
+# Hello World
+
+Install the **xaringan** package from [Github](https://github.com/yihui/xaringan):
+
+```{r eval=FALSE, tidy=FALSE}
+devtools::install_github("yihui/xaringan")
+```
+
+--
+
+You are recommended to use the [RStudio IDE](https://www.rstudio.com/products/rstudio/), but you do not have to.
+
+- Create a new R Markdown document from the menu `File -> New File -> R Markdown -> From Template -> Ninja Presentation`;<sup>1</sup>
+
+--
+
+- Click the `Knit` button to compile it;
+
+--
+
+- or use the [RStudio Addin](https://rstudio.github.io/rstudioaddins/)<sup>2</sup> "Infinite Moon Reader" to live preview the slides (every time you update and save the Rmd document, the slides will be automatically reloaded in RStudio Viewer.
+
+.footnote[
+[1] 中文用户请看[这份教程](http://slides.yihui.name/xaringan/zh-CN.html)
+
+[2] See [#2](https://github.com/yihui/xaringan/issues/2) if you do not see the template or addin in RStudio.
+]
+
+---
+background-image: url(`r xaringan:::karl`)
+background-position: 50% 50%
+class: center, bottom, inverse
+
+# You only live once!
+
+---
+
+# Hello Ninja
+
+As a presentation ninja, you certainly should not be satisfied by the "Hello World" example. You need to understand more about two things:
+
+1. The [remark.js](https://remarkjs.com) library;
+
+1. The **xaringan** package;
+
+Basically **xaringan** injected the chakra of R Markdown (minus Pandoc) into **remark.js**. The slides are rendered by remark.js in the web browser, and the Markdown source needed by remark.js is generated from R Markdown (**knitr**).
+
+---
+
+# remark.js
+
+You can see an introduction of remark.js from [its homepage](https://remarkjs.com). You should read the [remark.js Wiki](https://github.com/gnab/remark/wiki) at least once to know how to
+
+- create a new slide (Markdown syntax<sup>*</sup> and slide properties);
+
+- format a slide (e.g. text alignment);
+
+- configure the slideshow;
+
+- and use the presentation (keyboard shortcuts).
+
+It is important to be familiar with remark.js before you can understand the options in **xaringan**.
+
+.footnote[[*] It is different with Pandoc's Markdown! It is limited but should be enough for presentation purposes. Come on... You do not need a slide for the Table of Contents! Well, the Markdown support in remark.js [may be improved](https://github.com/gnab/remark/issues/142) in the future.]
+
+---
+background-image: url(`r xaringan:::karl`)
+background-size: cover
+class: center, bottom, inverse
+
+# I was so happy to have discovered remark.js!
+
+---
+class: inverse, middle, center
+
+# Using xaringan
+
+---
+
+# xaringan
+
+Provides an R Markdown output format `xaringan::moon_reader` as a wrapper for remark.js, and you can use it in the YAML metadata, e.g.
+
+```yaml
+---
+title: "A Cool Presentation"
+output:
+  xaringan::moon_reader
+    yolo: true
+    nature:
+      autoplay: 30000
+---
+```
+
+See the help page `?xaringan::moon_reader` for all possible options that you can use.
+
+---
+
+# remark.js vs xaringan
+
+Some differences between using remark.js (left) and using **xaringan** (right):
+
+.pull-left[
+1. Start with a boilerplate HTML file;
+
+1. Plain Markdown;
+
+1. Write JavaScript to autoplay slides;
+
+1. Manually configure MathJax;
+
+1. Highlight code with `*`;
+
+1. Edit Markdown source and refresh browser to see updated slides;
+]
+
+.pull-right[
+1. Start with an R Markdown document;
+
+1. R Markdown (can embed R/other code chunks);
+
+1. Provide an option `autoplay`;
+
+1. MathJax just works;<sup>*</sup>
+
+1. Highlight code with `{{}}`;
+
+1. The RStudio addin "Infinite Moon Reader" automatically refreshes slides on changes;
+]
+
+.footnote[[*] Not really. See next page.]
+
+---
+
+# Math Expressions
+
+You can write LaTeX math expressions inside a pair of dollar signs, e.g. &#36;\alpha+\beta$ renders $\alpha+\beta$. You can use the display style with double dollar signs:
+
+```
+$$\bar{X}=\frac{1}{n}\sum_{i=1}^nX_i$$
+```
+
+$$\bar{X}=\frac{1}{n}\sum_{i=1}^nX_i$$
+
+Limitations:
+
+1. The source code of a LaTeX math expression must be in one line, unless it is inside a pair of double dollar signs, in which case the starting `$$` must appear in the very beginning of a line, followed immediately by a non-space character, and the ending `$$` must be at the end of a line, led by a non-space character;
+
+1. There should not be spaces after the opening `$` or before the closing `$`.
+
+1. Math does not work on the title slide (see [#61](https://github.com/yihui/xaringan/issues/61) for a workaround).
+
+---
+
+# R Code
+
+```{r comment='#'}
+# a boring regression
+fit = lm(dist ~ 1 + speed, data = cars)
+coef(summary(fit))
+dojutsu = c('地爆天星', '天照', '加具土命', '神威', '須佐能乎', '無限月読')
+grep('天', dojutsu, value = TRUE)
+```
+
+---
+
+# R Plots
+
+```{r cars, fig.height=4, dev='svg'}
+par(mar = c(4, 4, 1, .1))
+plot(cars, pch = 19, col = 'darkgray', las = 1)
+abline(fit, lwd = 2)
+```
+
+---
+
+# Tables
+
+If you want to generate a table, make sure it is in the HTML format (instead of Markdown or other formats), e.g.,
+
+```{r}
+knitr::kable(head(iris), format = 'html')
+```
+
+---
+
+# HTML Widgets
+
+I have not thoroughly tested HTML widgets against **xaringan**. Some may work well, and some may not. It is a little tricky.
+
+Similarly, the Shiny mode (`runtime: shiny`) does not work. I might get these issues fixed in the future, but these are not of high priority to me. I never turn my presentation into a Shiny app. When I need to demonstrate more complicated examples, I just launch them separately. It is convenient to share slides with other people when they are plain HTML/JS applications.
+
+See the next page for two HTML widgets.
+
+---
+
+```{r out.width='100%', fig.height=6, eval=require('leaflet')}
+library(leaflet)
+leaflet() %>% addTiles() %>% setView(-93.65, 42.0285, zoom = 17)
+```
+
+---
+
+```{r eval=require('DT'), tidy=FALSE}
+DT::datatable(
+  head(iris, 10),
+  fillContainer = FALSE, options = list(pageLength = 8)
+)
+```
+
+---
+
+# Some Tips
+
+- When you use the "Infinite Moon Reader" addin in RStudio, your R session will be blocked by default. You can click the red button on the right of the console to stop serving the slides, or use the _daemonized_ mode so that it does not block your R session. To do the latter, you can set the option
+
+    ```r
+    options(servr.daemon = TRUE)
+    ```
+    
+    in your current R session, or in `~/.Rprofile` so that it is applied to all future R sessions. I do the latter by myself.
+    
+    To know more about the web server, see the [**servr**](https://github.com/yihui/servr) package.
+
+--
+
+- Do not forget to try the `yolo` option of `xaringan::moon_reader`.
+
+    ```yaml
+    output:
+      xaringan::moon_reader:
+        yolo: true
+    ```
+
+---
+
+# Some Tips
+
+- Slides can be automatically played if you set the `autoplay` option under `nature`, e.g. go to the next slide every 30 seconds in a lightning talk:
+
+    ```yaml
+    output:
+      xaringan::moon_reader:
+        nature:
+          autoplay: 30000
+    ```
+
+--
+
+- A countdown timer can be added to every page of the slides using the `countdown` option under `nature`, e.g. if you want to spend one minute on every page when you give the talk, you can set:
+
+    ```yaml
+    output:
+      xaringan::moon_reader:
+        nature:
+          countdown: 60000
+    ```
+
+    Then you will see a timer counting down from `01:00`, to `00:59`, `00:58`, ... When the time is out, the timer will continue but the time turns red.
+
+---
+
+# Some Tips
+
+- There are several ways to build incremental slides. See [this presentation](https://slides.yihui.name/xaringan/incremental.html) for examples.
+
+- The option `highlightLines: true` of `nature` will highlight code lines that start with `*`, or are wrapped in `{{ }}`, or have trailing comments `#<<`;
+
+    ```yaml
+    output:
+      xaringan::moon_reader:
+        nature:
+          highlightLines: true
+    ```
+
+    See examples on the next page.
+
+---
+
+# Some Tips
+
+
+.pull-left[
+An example using a leading `*`:
+
+    ```r
+    if (TRUE) {
+    ** message("Very important!")
+    }
+    ```
+Output:
+```r
+if (TRUE) {
+* message("Very important!")
+}
+```
+
+This is invalid R code, so it is a plain fenced code block that is not executed.
+]
+
+.pull-right[
+An example using `{{}}`:
+
+    `r ''````{r tidy=FALSE}
+    if (TRUE) {
+    *{{ message("Very important!") }}
+    }
+    ```
+Output:
+```{r tidy=FALSE}
+if (TRUE) {
+{{ message("Very important!") }}
+}
+```
+
+It is valid R code so you can run it. Note that `{{}}` can wrap an R expression of multiple lines.
+]
+
+---
+
+# Some Tips
+
+An example of using the trailing comment `#<<` to highlight lines:
+
+````markdown
+`r ''````{r tidy=FALSE}
+library(ggplot2)
+ggplot(mtcars) + 
+  aes(mpg, disp) + 
+  geom_point() +   #<<
+  geom_smooth()    #<<
+```
+````
+
+Output:
+
+```{r tidy=FALSE, eval=FALSE}
+library(ggplot2)
+ggplot(mtcars) + 
+  aes(mpg, disp) + 
+  geom_point() +   #<<
+  geom_smooth()    #<<
+```
+
+---
+
+# Some Tips
+
+- To make slides work offline, you need to download a copy of remark.js in advance, because **xaringan** uses the online version by default (see the help page `?xaringan::moon_reader`).
+
+- You can use `xaringan::summon_remark()` to download the latest or a specified version of remark.js. By default, it is downloaded to `libs/remark-latest.min.js`.
+
+- Then change the `chakra` option in YAML to point to this file, e.g.
+
+    ```yaml
+    output:
+      xaringan::moon_reader:
+        chakra: libs/remark-latest.min.js
+    ```
+
+- If you used Google fonts in slides (the default theme uses _Yanone Kaffeesatz_, _Droid Serif_, and _Source Code Pro_), they won't work offline unless you download or install them locally. The Heroku app [google-webfonts-helper](https://google-webfonts-helper.herokuapp.com/fonts) can help you download fonts and generate the necessary CSS.
+
+---
+
+# Macros
+
+- remark.js [allows users to define custom macros](https://github.com/yihui/xaringan/issues/80) (JS functions) that can be applied to Markdown text using the syntax `![:macroName arg1, arg2, ...]` or `![:macroName arg1, arg2, ...](this)`. For example, before remark.js initializes the slides, you can define a macro named `scale`:
+
+    ```js
+    remark.macros.scale = function (percentage) {
+      var url = this;
+      return '<img src="' + url + '" style="width: ' + percentage + '" />';
+    };
+    ```
+
+    Then the Markdown text
+
+    ```markdown
+    ![:scale 50%](image.jpg)
+    ```
+
+    will be translated to
+    
+    ```html
+    <img src="image.jpg" style="width: 50%" />
+    ```
+
+---
+
+# Macros (continued)
+
+- To insert macros in **xaringan** slides, you can use the option `beforeInit` under the option `nature`, e.g.,
+
+    ```yaml
+    output:
+      xaringan::moon_reader:
+        nature:
+          beforeInit: "macros.js"
+    ```
+
+    You save your remark.js macros in the file `macros.js`.
+
+- The `beforeInit` option can be used to insert arbitrary JS code before `remark.create()`. Inserting macros is just one of its possible applications.
+
+---
+
+# CSS
+
+Among all options in `xaringan::moon_reader`, the most challenging but perhaps also the most rewarding one is `css`, because it allows you to customize the appearance of your slides using any CSS rules or hacks you know.
+
+You can see the default CSS file [here](https://github.com/yihui/xaringan/blob/master/inst/rmarkdown/templates/xaringan/resources/default.css). You can completely replace it with your own CSS files, or define new rules to override the default. See the help page `?xaringan::moon_reader` for more information.
+
+---
+
+# CSS
+
+For example, suppose you want to change the font for code from the default "Source Code Pro" to "Ubuntu Mono". You can create a CSS file named, say, `ubuntu-mono.css`:
+
+```css
+@import url(https://fonts.googleapis.com/css?family=Ubuntu+Mono:400,700,400italic);
+
+.remark-code, .remark-inline-code { font-family: 'Ubuntu Mono'; }
+```
+
+Then set the `css` option in the YAML metadata:
+
+```yaml
+output:
+  xaringan::moon_reader:
+    css: ["default", "ubuntu-mono.css"]
+```
+
+Here I assume `ubuntu-mono.css` is under the same directory as your Rmd.
+
+See [yihui/xaringan#83](https://github.com/yihui/xaringan/issues/83) for an example of using the [Fira Code](https://github.com/tonsky/FiraCode) font, which supports ligatures in program code.
+
+---
+
+# Themes
+
+Don't want to learn CSS? Okay, you can use some user-contributed themes. A theme typically consists of two CSS files `foo.css` and `foo-fonts.css`, where `foo` is the theme name. Below are some existing themes:
+
+```{r}
+names(xaringan:::list_css())
+```
+
+To use a theme, you can specify the `css` option as an array of CSS filenames (without the `.css` extensions), e.g.,
+
+```yaml
+output:
+  xaringan::moon_reader:
+    css: [default, metropolis, metropolis-fonts]
+```
+
+If you want to contribute a theme to **xaringan**, please read [this blog post](https://yihui.name/en/2017/10/xaringan-themes).
+
+---
+class: inverse, middle, center
+background-image: url(https://upload.wikimedia.org/wikipedia/commons/3/39/Naruto_Shiki_Fujin.svg)
+background-size: contain
+
+# Naruto
+
+---
+background-image: url(https://upload.wikimedia.org/wikipedia/commons/b/be/Sharingan_triple.svg)
+background-size: 100px
+background-position: 90% 8%
+
+# Sharingan
+
+The R package name **xaringan** was derived<sup>1</sup> from **Sharingan**, a dōjutsu in the Japanese anime _Naruto_ with two abilities:
+
+- the "Eye of Insight"
+
+- the "Eye of Hypnotism"
+
+I think a presentation is basically a way to communicate insights to the audience, and a great presentation may even "hypnotize" the audience.<sup>2,3</sup>
+
+.footnote[
+[1] In Chinese, the pronounciation of _X_ is _Sh_ /ʃ/ (as in _shrimp_). Now you should have a better idea of how to pronounce my last name _Xie_.
+
+[2] By comparison, bad presentations only put the audience to sleep.
+
+[3] Personally I find that setting background images for slides is a killer feature of remark.js. It is an effective way to bring visual impact into your presentations.
+]
+
+---
+
+# Naruto terminology
+
+The **xaringan** package borrowed a few terms from Naruto, such as
+
+- [Sharingan](http://naruto.wikia.com/wiki/Sharingan) (写輪眼; the package name)
+
+- The [moon reader](http://naruto.wikia.com/wiki/Moon_Reader) (月読; an attractive R Markdown output format)
+
+- [Chakra](http://naruto.wikia.com/wiki/Chakra) (查克拉; the path to the remark.js library, which is the power to drive the presentation)
+
+- [Nature transformation](http://naruto.wikia.com/wiki/Nature_Transformation) (性質変化; transform the chakra by setting different options)
+
+- The [infinite moon reader](http://naruto.wikia.com/wiki/Infinite_Tsukuyomi) (無限月読; start a local web server to continuously serve your slides)
+
+- The [summoning technique](http://naruto.wikia.com/wiki/Summoning_Technique) (download remark.js from the web)
+
+You can click the links to know more about them if you want. The jutsu "Moon Reader" may seem a little evil, but that does not mean your slides are evil.
+
+---
+
+class: center
+
+# Hand seals (印)
+
+Press `h` or `?` to see the possible ninjutsu you can use in remark.js.
+
+![](https://upload.wikimedia.org/wikipedia/commons/7/7e/Mudra-Naruto-KageBunshin.svg)
+
+---
+
+class: center, middle
+
+# Thanks!
+
+Slides created via the R package [**xaringan**](https://github.com/yihui/xaringan).
+
+The chakra comes from [remark.js](https://remarkjs.com), [**knitr**](http://yihui.name/knitr), and [R Markdown](https://rmarkdown.rstudio.com).

inst/rmarkdown/templates/xaringanthemer/template.yaml

+name: Ninja Themed Presentation
+description: >
+  Create a themed presentation using the xaringanthemer package, to make a
+  xaringan presentation based on remark.js.
+create_dir: false