Added Python3 support. Now Python 2 or 3 can be used with the same code

The code is runnable with Python3 and Python2 now. Tested with Python 2.7 and Python 3.3.
Please write code in the future for Python 2 and 3, so both are supported
python2 also has io: https://docs.python.org/2.6/library/io.html

so, if there is no good reason to keep StringIO, we maybe can just use io for both pythons.