PyPi packaging

[philip-sterne]

This would be much easier to use if the code adopted the standard python packaging structure:
http://python-packaging.readthedocs.io/en/latest/minimal.html

Basically, stick all the meaningful code inside another "minsketch" directory and add a pretty minimal setup.py file (as shown in the link).

[guydav]

After the next commit, this will mostly be complete, aside from an issue in the interplay between read the docs and python dependencies. As I'm not quite sure how to resolve it, I opened an issue against RTD to clarify how it should be done:

readthedocs/readthedocs.org#2549