Python 3 port?

I'm working on a project in Python 3 and would like to use mrjob. I began attempting to port what I could, but it would really benefit from the experience of someone more familiar with the project (and porting to Python 3 in general)!

I started using `2to3` to port the main package and tests, and have been working on porting things going through each set of tests. Most of the issues it seems are string/bytes related.

Hopefully this is helpful – it would be nice to have a Python 3 branch to work off of :)