Added --noschema option to createdb for use with --migrate. Disables moving schema to allow for multiple bots/prefixes.

Signed-off-by: Martin Stone <martin@d7415.co.uk>
(cherry picked from commit 608640e6b609c716eaabe74c6b4c0f38eb6ae332)
README.md: Added notes about multi-bot support.

Signed-off-by: Martin Stone <martin@d7415.co.uk>
(cherry picked from commit c8c4fa8b11697a4481f1deeb9b41e4cccd62881f)
createdb: Added "--from-legacy" option to upgrade tables to acl format.

Signed-off-by: Martin Stone <martin@d7415.co.uk>
README.md: Some references to the new access system.

Signed-off-by: Martin Stone <martin@d7415.co.uk>