Enable building videojs with browserify.

This uses browserify-shim to get browserify to recognize videojs.
It uses dist/video-js/video.js for the main file of the module.
To build using browserify, you just run browserify on the module and
use --standalone (or -s) to make it produce a UMD file.
This seems to work just fine in the browser (and requirejs looks like
it'll work, though, I haven't tested it) but it won't work in node right
now because videojs is doing a lot of stuff with 'document' directly and
its causing problems in node.