Python 3 Support

[kbourgoin]

Possibly not going into 0.8.2-01, but we should be sure to not forget about this.

[emmettbutler]

Work in progress #144

[mcandre]

+1

[emmettbutler]

A lot has happened since work on this started, and the current most promising pull request is here thanks to @sontek. Figuring out a testing workflow around this will be my first priority once #177 is merged.

[emmettbutler]

@sontek's branch is looking pretty good now - as far as I'm concerned it's ready for merging. We'll need to add a bit of documentation about the preferred way to run tests under three interpreters.

[rduplain]

#231