Support for lists

Hi Matt,
I added medium-style support for ordered and unordered lists — works fine in firefox & chrome. There's no support for increasing or decreasing the indentation level, I don't know if or how you planned on doing this.

Also noteworthy, when breaking out of a list using carriage returns, Chrome places the carret inside a new empty div, firefox inside a p. I don't know if you planned on adressing this kind of cross-browser issues.

Cheers,
Yannick