Fix parsing of raw strings containing unclosed parentheses and brackets

Strings like r'[' and r'(' were causing the rest of the document to be
parsed as if it were inside the regex. Now we terminate the regex at the
closing quote in all cases.

This is a backport of
https://github.com/textmate/python.tmbundle/commit/2567262452b389f7042ef3026e0443f6336d1735
Make sure things other than regexes get parsed inside raw strings

My CSON formatting was bad, which caused only the regular expression
grammar to get parsed inside of raw strings.
Merge pull request #37 from aroben/fix-unclosed-regexes

Fix parsing of raw strings containing unclosed parentheses and brackets