pkgdown: put articles with child chunks back in vignettes/

.Rbuildignore

 ^appveyor\.yml$
 ^\.travis\.yml$
 ^pkgdown$
+^vignettes/fonts\.Rmd$
+^vignettes/themes\.Rmd$

pkgdown/_pkgdown.yml

 - title: xaringan Themes
   desc: |
     Parameterized styles for xaringan slides using one (mono)
-    or two (duo) base colors. Bonus: slide styles base on the
+    or two (duo) base colors. Bonus: slide styles based on the
     solarized color palette.
   contents:
     - starts_with("style_mono")
       href: reference/index.html
     themes:
       text: Themes
-      href: articles/singles/themes.html
+      href: articles/themes.html
     fonts:
       text: Fonts
-      href: articles/singles/fonts.html
+      href: articles/fonts.html
     template-vars:
       text: Template Variables
       href: articles/template-variables.html

vignettes/singles/fonts.Rmd → vignettes/fonts.Rmd

 tvv <- xaringanthemer:::template_variables$variable
 ```
 
-```{r child="../../man/fragments/_fonts.Rmd"}
+```{r child="../man/fragments/_fonts.Rmd"}
 ```

vignettes/singles/themes.Rmd → vignettes/themes.Rmd

 knitr::opts_chunk$set(results = "asis", echo=FALSE)
 ```
 
-```{r child="../../man/fragments/_themes.Rmd"}
+```{r child="../man/fragments/_themes.Rmd"}
 ```