API specification in source tree

Note: this blueprint has been refocused to just worry about API documentation, so ignore the comments below about "General documentation" and "Developer Documentation". Administrator docs is now being tracked in another BP: https://blueprints.launchpad.net/quantum/+spec/quantum-admin-docs . A place-holder blueprint for developer docs is here: https://blueprints.launchpad.net/quantum/+spec/quantum-developer-docs

The goal of this blueprint is to have API specification within Quantum source code tree.

API specification and uses case are currently in the Openstack wiki.
Moving them in the source code tree will have several benefits, mainly the ability of allowing the standard revieew process to be applied to the API specification in the same way as it is currently applied to code.

The implementation for this blueprint will not generate the API spefication directly from docstrings in code.
This could be however considered in the future.

The implementation for this blueprint will provide:
- a basic framework for project documentation
- a skeleton of rst files for general information and developer documentation
    - General documentation :
        - Installation
        - Integration with nova
        - CLI user guide
        - Use cases
    - Developer documentation:
        - Plugin development guide
        - Module documentation (generated from docstring)
- Full DocBook documentation for API specification