2.0.0

---

• Implement .shutdown(immediate=False) for both sync and async APIs #720

  The change is not fully backward compatible:

  1. If the queue is closed, janus.AsyncQueueShutDown and
     janus.SyncQueueShutDown exceptions are raised instead of RuntimeError.

  2. Both sync and async .task_done() and .join() don't raise any exception
     on queue shutdown/closing anymore; it is compatible with shutdown behavior
     of stdlib sync and async queues.