BitArray The Final Act

Alas, there's the 3rd and last video about BitArray, originated on my spark of inspiration on a Caltrain ride home. This makes my first YouTube playlist as well, even tho the first 2 videos were planned to be completely separate.

We added more standard library functionalities to BitArray (ExpressibleByArrayLiteral, CustomStringConvertible, Equatable, etc). Then, we added documentation and other open-source things left undone from "episode 2".