Refactoring and some small improvements

[akamgm]

A few changes:

• Separate highlighting for builtins vs user-defined operators
• "Redirects" are highlighted as variables
• Add string highlighting, including bare strings between operators/comments

One regression currently: TODO/FIXME/etc are highlighting as comments rather than documentation - have to fix this

[akamgm]

@dovinmu - please take a look and see if you think this is a good direction