Make a OPTIONS_GHC yasnippet completion

Similar to the [`lang` LANGUAGE](https://github.com/haskell/haskell-mode/blob/master/snippets/haskell-mode/lang-pragma) pragma completion, create a [OPTIONS-GHC](https://downloads.haskell.org/~ghc/7.0.3/docs/html/users_guide/ch04s02.html#source-file-options) pragma completion. Per issue #444 .
