Add support for Dune (#4263)

* Add support for dune

* Add test

* Undo reformatting of Markdown file

* Refer to ale-ocaml-dune from ale.txt

doc/ale-ocaml.txt

@@ -2,6 +2,26 @@
 ALE OCaml Integration                                       *ale-ocaml-options*
 
 
+===============================================================================
+dune                                                           *ale-ocaml-dune*
+
+  Dune is a build system for OCaml projects. The `dune format` command is
+  supported for automatically formatting `dune` and `dune-project` files.
+
+g:ale_ocaml_dune_executable                       *g:ale_ocaml_dune_executable*
+                                                  *b:ale_ocaml_dune_executable*
+  Type: |String|
+  Default: `'dune'`
+
+  This variable can be set to pass the path to dune.
+
+g:ale_ocaml_dune_options                             *g:ale_ocaml_dune_options*
+                                                     *b:ale_ocaml_dune_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be set to pass additional options to the dune fixer.
+
 ===============================================================================
 merlin                                                       *ale-ocaml-merlin*
 

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

@@ -386,6 +386,7 @@ Notes:
   * `clangd`
   * `uncrustify`
 * OCaml
+  * `dune`
   * `merlin` (see |ale-ocaml-merlin|)
   * `ocamlformat`
   * `ocamllsp`

doc/ale.txt

@@ -3041,6 +3041,7 @@ documented in additional help files.
     clangd................................|ale-objcpp-clangd|
     uncrustify............................|ale-objcpp-uncrustify|
   ocaml...................................|ale-ocaml-options|
+    dune..................................|ale-ocaml-dune|
     merlin................................|ale-ocaml-merlin|
     ocamllsp..............................|ale-ocaml-ocamllsp|
     ols...................................|ale-ocaml-ols|