CouchDB: Changing insert to be an optional batch insert.

Disable by default. Option can easily overload the DB server, giving
503 errors. Use this option with caution.
CouchDB: Retry on seeing HTTP errors.

Changes to update, read, init, insert. Parametrize wait with a min and max
latency and double the wait every attempt till max latency is reached. Also
add a parameter for the total number of retries.