RabbitMQ exchanges and consume/non-consume queues.

It is now possible to use RabbitmqWriter and RabbitmqMonitor with exchanges.
Instead of specifying a queue, like before, specify

RabbitmqWriter(exchange="myexchange", ...)

The monitor can be set up to consume from the exchange or listen on its own exclusive queue.
For consuming, do

RabbitmqMonitor(exchange="myexchange", consuming=True, ...)

For non-consuming, set consuming=False.

(Not sure which should be the default, yet.)