Switch build system to Browserify

See https://github.com/audiocogs/aurora.js/pull/75
It's fine, just doesn't match all the other codecs which won't have the `.js` on the end, and the [npm docs](https://www.npmjs.org/doc/files/package.json.html) say it's not recommended. But idk what else we'd use. Could use upper case `FLAC` but that might be confusing since there is already a package with the lower case name.