Fix regex for syntax-highlighting of keywords

Hi there,

I don't know if it's only for me, but syntax highlighting for Doxygen-style comments doesn't work with C, C++ and other packages, as the regex which matches comments in those packages overrides the regex used by the Doxygen bundle. Therefore I introduced look-aheads and -behinds to detect, whether we're inside a comment.

Brackets with arguments to keywords were'nt matched either, so I extended the regex.

![example](https://cloud.githubusercontent.com/assets/932156/4338529/2a51666a-401a-11e4-8522-8282cccf2df4.png)

Would be glad if this would make it into master!

Best
Martin