Write an easy-to-use Python API client

[fangpenlin]

Although billy has a RESTful API, it is still better to have a easy-to-use Python API client library that the usage might like what I mentioned in #25.

However, this is not a priority task as the API may not be stable for a period. Also, we should take care of naming problem as billy is already used by the server project. Maybe we can use billy-client for Python project name (in PyPi and github repo). And for Python package name (the_name/init.py), we can use billy_client, or we can use a Python namespace package ( http://www.python.org/dev/peps/pep-0382/ ), make it under billy.client? Well, not priority, think about it later.

[mjallday]

In our internal projects we name the services xxx_service e.g. balanced_service since the client libraries are directly used by more people than the actual services that support them. Our individual client library repos end up being service-language e.g. balanced-python but the package name would simply be balanced.