pywt update, python 3 support, new numpy interface, refactoring

Hi @nigma, here's a large refactoring that adds single code base Python 3 support, a unit test suite, numpy-style docstrings, and a lot of changes to the internals. It should be fully backwards compatible.

I know this will not be trivial to review. And am actually not sure if this project is still active or not. If you're interested and want me to split this in a few parts, please let me know. Before doing that it would help if you could look at the overall structure of changes though to make sure you agree with those.