Add Python3 compatibility.

Maintain single code base support for Python 2.6, 2.7 and 3.3.
actually, keep unittest2 in requirements.txt to appease travis. for now.
remove anyjson from requirements.txt - actually should be installed by kombu (but isn't)
Ask Travis to check on Python 3.2 and 3.3

(and add self to AUTHORS)
Merge pull request #126 from adamgreig/py3

Python 3 Compatibility