Set up references to be shown in webpage.

Some still need additional information, and there are a few URLs that need to
be replaced with references, and the resulting rendering isn't great, but I'll
figure it out piece-by-piece.
Some previously-missing info on references.
Reworked citations to be links.

Decided that formal citations didn't work very well in the context of my notes,
so replaced them with links to relevant content (mostly source videos and
published papers).
Updated compiled output with latest sources.