Add support for --html
Only document things defined on the class itself, not on its parents
Add support for displaying class MROs and inherited members.

Also refactor some things. I should be able to get rid of the depenency on singledispatch now, although I might add it back in a bit.

(Note: singledispatch doesn't seem to work properly when passed old-style class objects, which was the main motivator in getting rid of it.)