add support for JSX syntax highlighting

[k4b7]

Since pygment lexers are essentially just a set of regexes it might be feasible run the JavaScript and the HTML lexers over the same JSX code.

@brownhead where do we use pygments? I couldn't find any reference to it other than in requirements.txt and env/lib/python2.7/site-packages.

[itsjohncs]

I think docutils (the library used to parse the RST) calls out to it.