Added download_url to github release

Added download_url, hopefully correct. I used [these instructions](http://peterdowns.com/posts/first-time-with-pypi.html). You will also need to tag the commit in order to generate a tarball at the url.

## Tag
    git pull
    git tag 0.1
    git push --tags

## Register package 

    python setup.py register -r PyPI-test

## Upload to PyPI Test

In your directory, run the command `python setup.py sdist upload -r PyPI-test`. You should get no errors, and should also now be able to see your library in the [test PyPI repository](http://testpypi.python.org/pypi).

## Upload to PyPI Live

    python setup.py register -r PyPI
    python setup.py sdist upload -r PyPI