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
hey valentin!

thanks for porting to python3! I have put some comments below, so the code can be improved / streamlined a bit.

For the _compat.py, see e.g. there:

https://github.com/mitsuhiko/flask/blob/master/flask/_compat.py

maybe also have a look at codereview.appspot.com - if you're doing bigger changes, you could get review before committing stuff, it is a bit more comfortable than here on github (use upload.py to upload stuff there).