Move simple constants from setup.py into setup.cfg

[pganssle]

Currently we specify a lot of string literals in our setup.py. We're trying to encourage people to use declarative build configurations wherever possible, so we might as well start off at home move as much as we can over to setup.cfg. Should be almost everything that is a simple string literal.

So in our setup.py, I would say we can move everything except:

1. dependency_links (Though I actually have no idea why those are in there in the first place)
2. entry_points: which dynamically reads the possible commands from some location somewhere.
3. package_data: Not sure what is going on with this, but it actually seems dangerous for our universal wheels produced on Linux... For now let's leave it alone.

[hpandeycodeit]

@pganssle I will work on this