Sass, bourbon, etc.

* Setup instructions which explicitly avoid inclusion of bourbon/neat in version control
* More or less copy-based the existing main.css into main.scss, then organized
* Removed many (but not all) references to pure

I no doubt missed a few styles but I migrated everything I ran into.
I'll also note that @theresaanna already suggested integrating grunt (and then gulp). She stopped making suggestions when I threw my hands up and left the room.