Fix various comment syntax highlighting cases

[jryans]

This fixes several comment syntax highlighting cases, including comments in:

• struct fields
• hash literal content
• function arguments

Fixes https://github.com/Eugleo/magic-racket/issues/71

[Eugleo]

Thanks! I'll push a new version this week.

[jryans]

@Eugleo It would be great to see this fix in a published version. If there's anything I can do to help out somehow, please let me know. 🙂