Enable spell checking in comments and doc strings

By doing so, the whole document no longer gets spell checked, only comments and doc strings. This was causing many keywords such as defmodule to be marked as misspelled.

Author: fphilipe

syntax/elixir.vim

@@ -12,7 +12,7 @@ syn sync minlines=2000
 
 syn cluster elixirNotTop contains=@elixirRegexSpecial,@elixirStringContained,@elixirDeclaration,elixirTodo,elixirArguments
 
-syn match elixirComment '#.*' contains=elixirTodo
+syn match elixirComment '#.*' contains=elixirTodo,@Spell
 syn keyword elixirTodo FIXME NOTE TODO OPTIMIZE XXX HACK contained
 
 syn keyword elixirKeyword case when cond for if unless try receive send
@@ -85,8 +85,8 @@ syn region elixirInterpolation matchgroup=elixirInterpolationDelimiter start="#{
 
 syn region elixirDocStringStart matchgroup=elixirDocString start=+"""+ end=+$+ oneline contains=ALLBUT,@elixirNotTop
 syn region elixirDocStringStart matchgroup=elixirDocString start=+'''+ end=+$+ oneline contains=ALLBUT,@elixirNotTop
-syn region elixirDocString start=+\z("""\)+ end=+^\s*\zs\z1+ contains=elixirDocStringStart,elixirTodo,elixirInterpolation fold keepend
-syn region elixirDocString start=+\z('''\)+ end=+^\s*\zs\z1+ contains=elixirDocStringStart,elixirTodo,elixirInterpolation fold keepend
+syn region elixirDocString start=+\z("""\)+ end=+^\s*\zs\z1+ contains=elixirDocStringStart,elixirTodo,elixirInterpolation,@Spell fold keepend
+syn region elixirDocString start=+\z('''\)+ end=+^\s*\zs\z1+ contains=elixirDocStringStart,elixirTodo,elixirInterpolation,@Spell fold keepend
 
 syn match elixirAtomInterpolated ':\("\)\@=' contains=elixirString
 syn match elixirString "\(\w\)\@<!?\%(\\\(x\d{1,2}\|\h{1,2}\h\@!\>\|0[0-7]{0,2}[0-7]\@!\>\|[^x0MC]\)\|(\\[MC]-)+\w\|[^\s\\]\)"