rds: additions

I plan to add the ability to create DB snapshots and restore a database from such a snapshot.

This would be done through adding the commands ‘snapshot’ and ‘restore’ and updating the appropriate docs.
As best I can I’ll minimise the necessary options by inferring as much as possible from the snapshot.

If anyone else has this (or other improvements) to the rds module in the works, let me know so that there are no clashes.

Hello I have added the ability to restore from a DB snapshot and have it in a pull request - https://github.com/ansible/ansible/pull/5388 as well.