Sphinx documentation linked with module inlines doc

This PR contains few things:
- add Readme a Development section
- add new doc file api-documentation.rst to document the API
- use locally same theme as used by RTD 'sphinx_rtd_theme'
- link Sphinx to the code documentation and start improve part of the client API

FYI, I think a good documentation for a client is RIAK we can use them as example for good practices, they have done a neat job on the documentation: http://basho.github.io/riak-python-client/index.html