Small syntax definition fixes and a new theme

I took your advice and forked. I updated the regexes for citation, math, and header matching. I also created a new theme. As of now, only my theme supports LaTeX highlighting, but I can update the other three themes if you like it.

TODO:
I tried to set up (i) table highlighting with a light gray background and (ii) automatically numbered lists, which are currently recognized as headers. 

For (i), I have a regex which will match pipe and grid tables: `((\+\-+)+\+(\n.+)*(\+\-+)+\+)|(((\|.*){2,}\n){2,})` but I think .tmLanguage doesn't like to match regexes over multiple lines. I could definitely figure out how to do it, probably with the \G symbol which I am yet to understand. However, the main utility of such highlighting would be to point out when a table is poorly constructed, and I'm not sure how you would do that with this system.

For (ii) I thought it would be as simple as adding a `#\.` every time I saw `^[ ]{0,3}([0-9]+\.|[a-z]\.)(?=\s)` but I guess it's not so simple…

Cheers