Add OPTIONS_HADDOCK snippet

Author: jdnavarro

Diff for: snippets/haskell.snippets

@@ -1,5 +1,7 @@
 snippet lang
 	{-# LANGUAGE ${0:OverloadedStrings} #-}
+snippet haddock
+	{-# OPTIONS_HADDOCK ${0:hide} #-}
 snippet info
 	-- |
 	-- Module      :  ${1:Module.Namespace}