Remove 2to3
Make python files 2/3 compatible

The changes are:
 * absolute imports
 * division (/ vs //)
 * use six for unicode/strings, dict.iter*
 * wrapping dict methods in lists where appropriate
Add six to setup_requires as setup.py test does not install install_requires
Fix py32 errors (hopefully got all of them)
Merge pull request #508 from aragilar/drop_2to3

Drop 2to3, make python files 2/3 compatible.