Add elm-format as a new fixer (#916)

* Add elm-format as a new fixer

doc/ale-elm.txt

@@ -0,0 +1,32 @@
+===============================================================================
+ALE Elm Integration                                           *ale-elm-options*
+
+
+===============================================================================
+elm-format                                                     *ale-elm-format*
+
+g:ale_elm_format_executable                       *g:ale_elm_format_executable*
+                                                  *b:ale_elm_format_executable*
+  Type: |String|
+  Default: `'elm-format'`
+
+  See |ale-integrations-local-executables|
+
+
+g:ale_elm_format_use_global                       *g:ale_elm_format_use_global*
+                                                  *b:ale_elm_format_use_global*
+  Type: |Number|
+  Default: `0`
+
+  See |ale-integrations-local-executables|
+
+
+g:ale_elm_format_options                             *g:ale_elm_format_options*
+                                                     *b:ale_elm_format_options*
+  Type: |String|
+  Default: `'--yes'`
+
+  This variable can be set to pass additional options to elm-format.
+
+===============================================================================
+  vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale.txt

@@ -217,7 +217,7 @@ Notes:
 * Dart: `dartanalyzer`
 * Dockerfile: `hadolint`
 * Elixir: `credo`, `dogma`!!
-* Elm: `elm-make`
+* Elm: `elm-make, elm-format`
 * Erb: `erb`, `erubis`
 * Erlang: `erlc`, `SyntaxErl`
 * Fortran: `gcc`