From time to time we get requests asking us to add support for new highlighting lexers, recognize additional extensions as certain languages, or ignore a directory from a repo's stats graph.
The code for these concerns was scattered around the app. I decided to unify and package them all up into a single library. Now it's open source.
So if you notice an unrecognized extension or you're really into some obscure language that isn't supported yet, now is your chance to help contribute back.