v0.30.1

This is a bugfix release with two changes:

• Properly do a graceful shutdown when the infrastructure informs us we are about to be shut down. If requests finish up fast enough, they won't be cut off in flight.
• Limit the size of the internal queue in the Kombu QueueConsumer. Previously, if the remote queue had a lot of messages this internal queue would fill up without bound and potentially consume excessive memory.