make python 3 compatible again
The function objects in python 3 have no `func_code` member anymore. Use `__code__` instead.
The byte objects in python 3 have no `format` method. Use `encode` instead.
The representation of the strings and encoded strings are different in python 2 and python 3 thus use PY3 from six.
Remove unlucky example from README since python 3 returns a float and python 2 an int in this situation
Python 2 and 3 build is working again