Log Message:
(devel/R-xfun) Updated 0.26 to 0.30

# CHANGES IN xfun VERSION 0.30

- Added a new function `is_blank()` (previously existed in **knitr**)
  to test if all elements of a character vector are blank (white
  spaces or empty strings).

- Added a new argument `error = TRUE` to `existing_files()`.

# CHANGES IN xfun VERSION 0.29

- `github_releases()` can fetch all releases (tags) of a Github repo
  now.

- Added an argument `.error` to `download_file()` so that users can
  customize the error message when the download fails.

- Added functions `rest_api_raw()` and `rest_api()` to get data from a
  REST API; also added the function `github_api()` to get data from
  the Github API based on `rest_api_raw()`.

- Added a wrapper function `system3()` based on `system2()` to mark
  the character output of `system2()` as UTF-8 if appropriate.

- Added a function `existing_files()` to return file paths that exist
  (a shorthand of `x[file.exists(x)]`).

- Added a function `read_all()` to read multiple files and concatenate
  the content into a character vector.

- `url_accessible()` uses `curlGetHeaders()` by default (instead of
  `download_file()`) to test if a URL is accessible when the **curl**
  package is not available.

- When `options(xfun.rev_check.compare = FALSE)`, `rev_check()` will
  run `R CMD check` on reverse dependencies against a source package
  but not the CRAN version of this package. By default, this option is
  `TRUE`, meaning that `R CMD check` will run against both versions of
  the package.

# CHANGES IN xfun VERSION 0.28

- Added a new function `url_accessible()` to test if a URL can be
  downloaded.

- Added a new function `try_error()` to try an expression and see if
  it throws an error.

# CHANGES IN xfun VERSION 0.27

- Exported and documented the function `xfun::base_pkgs()` (to return
  base R package names).

- Changed the default value of the `status_only` argument of
  `compare_Rcheck()` from `FALSE` to `TRUE`.

- Added new functions `crandalf_check()` and `crandalf_results()` for
  checking (especially large numbers of) reverse dependencies of
  packages via [**crandalf**](https://github.com/yihui/crandalf).

- Added new functions `append_utf8()` and `append_unique()` based on
  `read_utf8()` and `write_utf8()` to append content to files or
  connections.