(devel/R-xfun) Updated 0.31 to 0.35

# CHANGES IN xfun VERSION 0.35

- Added a new argument `token` to `protect_math()` to optionally
  include a token around math expressions.

- `base64_uri()` relies less on the **mime** package now. For some
  common file extensions (e.g., `.jpg`/`.png`), this function knows
  their MIME types.

- `stringsAsStrings()` has been removed from this package.

# CHANGES IN xfun VERSION 0.34

- Added a new function `alnum_id()` to generate ID strings from a character vector.

- The function `stringsAsStrings()` has been deprecated.

# CHANGES IN xfun VERSION 0.33

- Reverted the change for #68: the characters `-+!_#` are no longer
  accepted by default in filename extensions, since they are
  relatively rare and caused a breakage in rstudio/bookdown#1369. If
  you wish to allow for these characters, you may use the new `extra`
  argument in `file_ext()` and related functions, e.g.,
  `xfun::file_ext(x, extra = '-+!_#')`.

- The function `stringsAsStrings()` will be deprecated in a future
  release of **xfun**, because the global option `stringsAsFactors =
  FALSE` has become the default in base R since 4.0.0.

# CHANGES IN xfun VERSION 0.32

- Added a function `shrink_images()` to shrink images to a maximum
  width using the **magick** package (thanks, @apreshill,
  rstudio/blogdown#614).

- Added a function `tinify_dir()` as a wrapper of `tinify()` to
  compress images under a directory.

- `file_ext()` supports more file extensions now, such as `.c++`,
  `.FB2K-COMPONENT`, and so on (thanks, @tentacles-from-outer-space,
  #68).

- Fixed the issue that `xfun::base_pkgs()` could hang R (thanks,
  @mmaechler, #66).

- The `...` argument in `dir_create()` was not passed to `dir.create()`.

(mef)