New GitHub icons

Had a blast working alongside @Mark Otto @Emily and @Kim Estoesta on shipping the latest set of GitHub icons at Universe. Truly a great team effort! These were used as visual assets for all of the keynote presentations at the conference and are now part of our ever-expanding, badass icon system.

I also attached behind the scenes screenshots showing the "mess" Ahemm... exploration, progress, and some of the iterations behind each icon.