Improve Haskell Syntax Highlighting.

Haskell Syntax highlighting seems dull.

Currently all of these are one colour: functions/variables (definitions and use), brackets, types. As well as operators and keywords are also the same colour.

There only seems to be a total of 5 colours on screen

Haskell's "lack" of liveliness is probably related to the fact that functions and variables are the same thing syntactically.

Here is a comparison between Spacemacs and Oni.

Also, Oni reminds me of when I used gVim, so it could be an upstream issue.