Add __init__.py to all directory to export packages in order to python2.
All classes inherit from 'object' in python2.
Use external library 'python-dateutil' in order to suppor python2
Python2 doesn't support time zone offset with datetime strptime.
The easiest way is using python-dateutil
Modifies 'str' class to six.text_type in order to support python2
Use six.moves.urllib package to support python2