Split the ocaml filetype into several filetypes

Now ocamlinterface ocamllex and menhir types must be taken into account
as well. Menhir filetype is not included as there seem to be no plans to
include it and even then it would take a big effort.

The filetypes are introduced by
ocaml/vim-ocaml#61

CHANGES.md

@@ -5,6 +5,8 @@ merlin NEXT_VERSION
     - Add a "heap_mbytes" field to Merlin server responses to report heap usage (#1717)
     - Add cache stats to telemetry (#1711)
     - Add a query_num field to the `ocamlmerlin` responses to detect server crashes (#1716)
+  + editor modes
+    - vim: load merlin under the ocamlinterface and ocamllex filetypes (#1340)
 
 merlin 4.13
 ===========

vim/merlin/dune

@@ -13,9 +13,12 @@
         (ftdetect/merlin.vim as vim/ftdetect/merlin.vim)
         (ftplugin/merlin.vim as vim/ftplugin/merlin.vim)
         (ftplugin/ocaml.vim as vim/ftplugin/ocaml.vim)
+        (ftplugin/ocamlinterface.vim as vim/ftplugin/ocamlinterface.vim)
+        (ftplugin/ocamllex.vim as vim/ftplugin/ocamllex.vim)
         (ftplugin/omlet.vim as vim/ftplugin/omlet.vim)
         (ftplugin/reason.vim as vim/ftplugin/reason.vim)
         (plugin/merlin.vim as vim/plugin/merlin.vim)
         (syntax_checkers/ocaml/merlin.vim as vim/syntax_checkers/ocaml/merlin.vim)
+        (syntax_checkers/ocamlinterface/merlin.vim as vim/syntax_checkers/ocamlinterface/merlin.vim)
         (syntax_checkers/omlet/merlin.vim as vim/syntax_checkers/omlet/merlin.vim)
         (syntax/merlin.vim as vim/syntax/merlin.vim)))

vim/merlin/ftplugin/ocamlinterface.vim

@@ -0,0 +1,2 @@
+" Activate merlin on current buffer
+call merlin#Register()

vim/merlin/ftplugin/ocamllex.vim

@@ -0,0 +1,2 @@
+" Activate merlin on current buffer
+call merlin#Register()

vim/merlin/syntax_checkers/ocamlinterface/merlin.vim

@@ -0,0 +1,23 @@
+" Enable Syntastic support
+" Make sure syntax_checkers directory is on runtime path, then set
+" :let g:syntastic_ocamlinterface_checkers=['merlin']
+
+function! SyntaxCheckers_ocamlinterface_merlin_IsAvailable()
+  if !exists("*merlin#SelectBinary")
+    return 0
+  endif
+  try
+    let l:path = merlin#SelectBinary()
+    return executable(l:path)
+  catch
+    return 0
+  endtry
+endfunction
+
+function! SyntaxCheckers_ocamlinterface_merlin_GetLocList()
+  return merlin#ErrorLocList()
+endfunction
+
+call g:SyntasticRegistry.CreateAndRegisterChecker({
+    \ 'filetype': 'ocamlinterface',
+    \ 'name': 'merlin'})