Move most config from `setup.py` to `setup.cfg` to simplify static config management

[mbrukman]

We are currently using setup.py and have code to read in a README.md file as a string, but we don't need this to be in code, since none of our configuration is dynamic. Instead, we can have a very simple setup.py and move our config into a static setup.cfg instead.

Docs:

• https://packaging.python.org/en/latest/tutorials/packaging-projects/
• https://packaging.python.org/en/latest/guides/distributing-packages-using-setuptools/