Added Python 3 compatibility, without breaking Python 2.7

[proycon]

tests pass on Python 3 and 2.7

[michaeljones]

This is very cool, thanks for contributing. How do you feel about compatibility with 2.6 and below? I realise they are ancient but I feel some people might be stuck on them still. Do you feel that using six is reasonable for that? I don't have a lot of experience with this. This isn't an attempt to get you to do more work :) Just to share you thoughts!

Thanks again!
Michael

[proycon]

I don't have too much experience with six. Personally I think people should move away from Python 2 alltogther. Python 3 has been out of quite some years now. Most distributions will have Python 2.7 (even older ones like Ubuntu 12.04 LTS) so I think Python 2.6 support can be dropped relatively safely for many projects. I stopped supporting 2.6 on all of my own projects as well. People who do rely on it can always fall back to older releases.

[yuokada]

Hi, @michaeljones @proycon
I would like to use in python3.6.
When is this PR merged?