py3k installation fix

I fixed `setup.py` so that the package can be installed with Python3.

I wanted to install it with Py3 for automatic UTF-8 support. I don't know if you meant it to be compatible with Py2 and Py3, so I expect something may crash. If it does, I will try to make some compatibility fixes in another pull request and take care of the unit tests.

So far, it works fine and my fix seems to be harmless.