Add support for linting git commit message files (#1233)

doc/ale-gitcommit.txt

@@ -0,0 +1,42 @@
+===============================================================================
+ALE Git Commit Integration                              *ale-gitcommit-options*
+
+
+===============================================================================
+gitlint                                                 *ale-gitcommit-gitlint*
+
+g:ale_gitcommit_gitlint_executable         *g:ale_gitcommit_gitlint_executable*
+                                           *b:ale_gitcommit_gitlint_executable*
+  Type: |String|
+  Default: `'gitlint'`
+
+  This variable can be changed to modify the executable used for gitlint.
+
+
+g:ale_gitcommit_gitlint_options               *g:ale_gitcommit_gitlint_options*
+                                              *b:ale_gitcommit_gitlint_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be changed to add command-line arguments to the gitlint
+  invocation.
+
+  For example, to dinamically set the gitlint configuration file path, you
+  may want to set >
+
+  let g:ale_gitcommit_gitlint_options = '-C /home/user/.config/gitlint.ini'
+<
+
+g:ale_gitcommit_gitlint_use_global         *g:ale_gitcommit_gitlint_use_global*
+                                           *b:ale_gitcommit_gitlint_use_global*
+  Type: |Number|
+  Default: `0`
+
+  This variable controls whether or not ALE will search for gitlint in a
+  virtualenv directory first. If this variable is set to `1`, then ALE will
+  always use |g:ale_gitcommit_gitlint_executable| for the executable path.
+
+  Both variables can be set with `b:` buffer variables instead.
+
+===============================================================================
+  vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:

doc/ale.txt

@@ -68,6 +68,8 @@ CONTENTS                                                         *ale-contents*
       gcc.................................|ale-fortran-gcc|
     fusionscript..........................|ale-fuse-options|
       fusion-lint.........................|ale-fuse-fusionlint|
+    git commit............................|ale-gitcommit-options|
+      gitlint.............................|ale-gitcommit-gitlint|
     glsl..................................|ale-glsl-options|
       glslang.............................|ale-glsl-glslang|
       glslls..............................|ale-glsl-glslls|
@@ -300,6 +302,7 @@ Notes:
 * Erlang: `erlc`, `SyntaxErl`
 * Fortran: `gcc`
 * FusionScript: `fusion-lint`
+* Git Commit Messages: `gitlint`
 * GLSL: glslang, `glslls`
 * Go: `gofmt`, `goimports`, `go vet`, `golint`, `gometalinter`!!, `go build`!!, `gosimple`!!, `staticcheck`!!
 * GraphQL: `eslint`, `gqlint`