Remove unnecessary kwarg for better GitPython compatibility.
pip no longer installs pre-release versions by default.

https://pip.pypa.io/en/latest/reference/pip_install.html#pre-release-versions
Update setup.py

Corrected `url` which pointed to a 404 and added a `description` field because project description on `pip` search and `pypi` listing listed project as `UNKNOWN`
Merge pull request #3 from lowks/patch-1

Update setup.py
Merge pull request #1 from jianli/master

merge