Update theme_xaringan*() examples and safer sysfonts font adder

Seems Droid Serif is no longer "in" Google Fonts

Need to remove all the warnings from docs

R/ggplot2.R

 #' @examples
 #' if (requireNamespace("ggplot2", quietly = TRUE)) {
 #'   # Set xaringanthemer theme but save to tempfile
-#'   duo_accent(outfile = tempfile())
+#'   style_duo_accent(outfile = tempfile())
 #'
 #'   library(ggplot2)
 #'   ggplot(iris) +
 #' @examples
 #' if (requireNamespace("ggplot2", quietly = TRUE)) {
 #'   # Set xaringanthemer theme but save to tempfile
-#'   duo_accent(outfile = tempfile())
+#'   style_duo_accent(outfile = tempfile())
 #'
 #'   library(ggplot2)
 #'   ggplot(iris) +
       "Roboto", "Source Code Pro", "Yanone Kaffeesatz"
     )
     if (identical(google, TRUE) || is_default_font) {
-      sysfonts::font_add_google(family, ...)
+      tryCatch(
+        sysfonts::font_add_google(family, ...),
+        error = function(e) warning(e$message),
+        warning = function(w) warning(w$message)
+      )
     } else {
       warning(paste(
         "Please manually register fonts not served by Google Fonts.",

man/theme_xaringan.Rd

 \examples{
 if (requireNamespace("ggplot2", quietly = TRUE)) {
   # Set xaringanthemer theme but save to tempfile
-  duo_accent(outfile = tempfile())
+  style_duo_accent(outfile = tempfile())
 
   library(ggplot2)
   ggplot(iris) +

man/theme_xaringan_inverse.Rd

 \examples{
 if (requireNamespace("ggplot2", quietly = TRUE)) {
   # Set xaringanthemer theme but save to tempfile
-  duo_accent(outfile = tempfile())
+  style_duo_accent(outfile = tempfile())
 
   library(ggplot2)
   ggplot(iris) +