add python 3 support

Works for me on Python 3.3 and back to 2.6. If the intention is to support versions less than 2.6 then we should do something else. http://python3porting.com/noconv.html#supporting-the-print-function or documenting ``pip install  pycompletion==0.1.0`` for less than 2.6 and ``pip install  pycompletion==0.2.0`` for 2.6 or greater