Issue #11: Add a Python library

I have being using it for more than two months and all seems to work fine. And should not bother the C++ one, so I cannot see any reason for not reincorporating the python client to the mongodb.

There's a bunch of commits but none touch existing code except adding python-pymongo and mongodb (instead of mongodb-dev) as run dependencies and declare the package as a python one.

Tell me if you need any additional information or changes before merging, or if you prefer that I do in a new branch.