Move documentation to sphinx

[twiecki]

Specifically, it would be nice if we had an online manual.

[richafrank]

@twiecki Do you think sphinx would produce a better online manual than what mk-docs is currently producing for the github.io page? (Which features do we want?)

[twiecki]

@richafrank I'm happy with the current website, except that it's missing a manual from the doc strings of all functions.

[twiecki]

Relevant: http://nbsphinx.readthedocs.org/