Python 3 support

Following discussion on PR #32, this adds Python 3 support without any external dependencies. Python 2.6 and above and Python 3.3 and above should work; older versions will not.

The tests are passing on Python 2 and 3; I haven't tried the examples.
If it really is static, make it a @staticmethod and lose the self.
If the self must stay, lose the comment and sort out the spacing after the commas ;-)