8.91: added ->local_users to the pool object.
            fixed total client (local user limit) limit:client; broken since version 6.5.
            fire command events on user objects in conjunction with those on connection objects.
            implemented (most of) the parameter parser for new message objects.
            added new evented method for adding user commands which will eventually replace ->register_user_command().
            the magical %user_commands now eliminates the need for ->register_user_command() over a foreach.
            updated Evented::API::Engine and Evented::Object.