Update for python 3

[droemer7]

Updates the python wrapper to work with python 3, retaining backwards compatibility with python 2. It can either be installed with:

sudo python2 setup.py install sudo python3 setup.py install

No changes are made to test.py, so that will not run at all. This is intentional: in its current state, test.py is fundamentally broken and prints erroneous warnings about the range calculations. Fixing this problem is more involved and should be addressed by a different PR.