Font lock Role annotations

[mrBliss]

I just noticed #1056 and realised that Role annotations are also not properly font locked.

Some examples that demonstrate that GitHub's syntax highlighting has the same problem 😃:

{-# LANGUAGE RoleAnnotations #-}

type role Ptr representational
data Ptr a = Ptr Addr#

type role Foo nominal representational phantom
data Foo a b c = Foo a b

The role keyword must only be highlighted after type, analogous to family. But what about phantom, representational, and nominal? They are also special keywords in this particular context, but specifying a regex for this seems nontrivial.

[gracjan]

@mrBliss: Are you able to write a (failing) test case? Usually when a test case is there somebody comes along and fixes the issue.

[gracjan]

We can easily keywordize role. The specifiers seem to be more of a problem, we may look at this later.