Issue 61 python33 support

Hi,
I modified your source code working both 2.7.x and 3.3.x using [six](http://pythonhosted.org/six/) module.
Please review my PR and merge if possible.

Changes:
* renamed modules and attributes compatibility
* implemented parsing request header for 3.3.x
* and more. Please see [six](http://pythonhosted.org/six/) documentation.

Testing:
* passed tests with Python 2.7.5 and 3.3.3 on Mac.
* couldn't execute tests with Python 2.6.x because recurlytests.py is written with 2.7 format.
* no tests added or deleted.

Thanks.