Python3 compatible Version

Hi, I've made the effort to make pyswip python3 compatible.
At this point all the current Tests run successfully on my machine under ubuntu14.04 x64 and with python 2.7, 3.2 and 3.4
Maybe you can test it with more configurations to make sure my machine is not the only one it runs on.
But even if you don't want to apply all changes, there might still be some interesting ones ( e.g.: 0ca5915, 3cb43ba or 699cbdc).
Of course you shouldn't take 1cb2cca but I have no idea how to exclude it from the pull request... sorry, my bad