[tor-dev] use sphinx on stem

Hi Damian,

I explored sphinx and tried it on stem these days, and it seemed pretty handy. I think a good way to produce nice documentation for stem is to create a page for each module manually, write an introduction by hand, and use autoclass / autofunction / autoexception in the autodoc extension to create API docs. automodule seems too general and does not work well with module's docstring in stem since it is not written in reST format, so I don't like it. What do you suggest? And how's your progress now?

Cheers, Beck