More doc updates.

- general updates to index.rst
- add api quick-ref section to index.rst
- consolidate contributing/* to contributing.rst & dev-quickstart.rst
- remove broken :term: links in architecture.rst
- rename v1.rst -> api-spec-v1.rst

Change-Id: Ib02fb3f8c8e3c6450e74b3a6831795699b2ddf67