Switch from distutils to setuptools for wheels.

Dropping python 3.1 support because travis.

For some reason, travis is shitting the bed every time it tries to build
against 3.1. Manual testing sucks and hopefully nobody is using 3.1 anymore
anyway, so who cares.

Add python 3 trove classifiers.

Correcting `git describe` fallback behavior.

Making better errors in the cython-less case.