Add ocaml linter: merlin (#177)

* Add ocaml linter: merlin

* Add docs for ocaml-merlin integration.

* Remove annoying error message from ocaml merlin linter

* Update doc to list merlin linter

ale_linters/ocaml/merlin.vim

@@ -0,0 +1,19 @@
+" Author: Andrey Popp -- @andreypopp
+" Description: Report errors in OCaml code with Merlin
+
+if !exists('g:merlin')
+  finish
+endif
+
+function! ale_linters#ocaml#merlin#Handle(buffer, lines)
+  let l:errors = merlin#ErrorLocList()
+  return l:errors
+endfunction
+
+call ale#linter#Define('ocaml', {
+\   'name': 'merlin',
+\   'executable': 'ocamlmerlin',
+\   'command': 'true',
+\   'callback': 'ale_linters#ocaml#merlin#Handle',
+\})
+