Python 3 migration

[rhyolight]

Dan, it might help you to see how I got the nupic.cpp working in python 3 here:

Hot Gym running in Python 3 via nupic.cpp & pybind

Hey folks, I just got a python3 script running hot gym data through SP/TM using the pybind bindings in nupic.cpp! I put it in a repo so anyone can continue working on it. Some things to do: date encoding sdr classification