Create a docs with sphinx

Create a sphinx documentation.

To generate a local doc do it:

1. git checkout docs
2. pip install -r requirements.txt
3. cd docs
4. make html

Now you can see the doc run a simple http server.

1.  cd build/html
2. python -m SimpleHTTPServer 9000

Open you browser and access localhost:9000

This commit its about the issue https://github.com/vandersonmota/model_mommy/issues/74
and is not done.