Comprehensive regular expression support

Whew! This was masochistic. 98% of the patterns should be covered here. (I skipped `\Q..\E` patterns because I wasn't sure the best way to handle them.) Overall, I think this is much more comprehensive than other language syntax files I've seen. It will be fun updating my color scheme to take advantage of them. 

Most of the new syntax groups are linked to `Special` because that seemed to make the most sense.

Alright! I'm gonna take a little break from this now and check back later.