Reinstate Python 3.x support.

- Don't use 2to3 -- it isn't needed.
- Uses six instead of ad-hoc compatibility hack.
- Fixes some issues around strictness of integer indexing.
- Update docs about supported versions of Python.
- Rename test.py to test_basic.py, since py.test won't pick it up with
  the old name (though nosetests did).
Added nitpicky = True to catch more errors
Replaced automodule with automodapi
Merge branch 'python3-fixes' of https://github.com/mdboom/sphere into mdboom-python3-fixes
Merge branch 'mdboom-python3-fixes'
they look fine to me