Reworks __version__ imports in setup.py. Fixes issue #111.

This is a fix. I used this suggestion:

http://stackoverflow.com/questions/458550/standard-way-to-embed-version-into-python-package

It works, but I'm not super fond of it because of the exec() call. It seems like there would be a simple and elegant way to do this. Some suggested package_resources but that only works inside your main `__init__.py` if you install the software first. It doesn't work if you want to just work from the install dir.