* remove online_schema_migration_examples since they overlap
with a section in the best practices doc
* move developer docs to doc/source/devref and rename where
appropriate
* moved content in developer.rst around, so the more often used
functions (releasenotes, docs, sample config and tests are
near the top).
* general clean up
Change-Id: If00b6535564644ff1f5b78e232edbac5d6e686f0
41bb06a69e