Add a fixer for r based on the styler package (#2401)

* Add styler as a new fixer for R files
* Add to the list of supported tools
* Add documentation

doc/ale-r.txt

@@ -25,5 +25,21 @@ g:ale_r_lintr_lint_package                         *g:ale_r_lintr_lint_package*
   of `lintr::lint`. This prevents erroneous namespace warnings when linting 
   package files.
 
+
+===============================================================================
+styler                                                           *ale-r-styler*
+
+g:ale_r_styler_options                                 *g:ale_r_styler_options*
+                                                       *b:ale_r_styler_options*
+  Type: |String|
+  Default: `'styler::tidyverse_style'`
+
+  This option can be configured to change the options for styler.
+
+  The value of this option will be used as the `style` argument for the 
+  `styler::style_file` options. Consult the styler documentation 
+  for more information.
+
+
 ===============================================================================
   vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale-supported-languages-and-tools.txt

@@ -357,6 +357,7 @@ Notes:
   * `qmllint`
 * R
   * `lintr`
+  * `styler`
 * Racket
   * `raco`
 * ReasonML

doc/ale.txt

@@ -2149,6 +2149,7 @@ documented in additional help files.
     qmlfmt................................|ale-qml-qmlfmt|
   r.......................................|ale-r-options|
     lintr.................................|ale-r-lintr|
+    styler................................|ale-r-styler|
   reasonml................................|ale-reasonml-options|
     merlin................................|ale-reasonml-merlin|
     ols...................................|ale-reasonml-ols|