Create a proper setup script

[rodluger]

The setup script for vspace should use setuptools, as in

https://github.com/VirtualPlanetaryLaboratory/bigplanet/blob/master/setup.py

The current setup script doesn't allow vspace to be listed as a dependency of vplanet since setuptools doesn't recognize it as a valid Python package.

[caitlyn-wilhelm]

Should be fixed now on the master branch!