Capture defp? as meta to get different coloring

Capture `def` and `defp` as meta in the language syntax to get different coloring. This is consistent with
how other languages such as Erlang and Python for instance color function names in their definition blocks in Sublime.

Note: I'm using a rather simplistic theme, so this might/might not affect other people.
This is tricky because it is not only def, defp, but also defmacro and defmacrop. We should also consider there are other macros like defdelegate, so I am not sure if this is worth it. :)