Python 3 compatibility (initial pass)

Brings simultaneous Python 2 and 3 support to nearly all of the codebase. Tests now run in parallel on Python 2.7 and 3.4. All dev and prod dependencies fully support both versions. Deployment has to take place on Python 2 (because Fabric ugh), but deploys into Python 3.

Does a lot of the work for #16, but doesn't fully resolve it (#9 is a blocker).