Prefetch support

[asix1337]

Hey, prefetch support like in celery would be great.

http://www.squaremobius.net/amqp.node/channel_api.html#channel_prefetch https://docs.celeryproject.org/en/stable/userguide/configuration.html#std:setting-worker_prefetch_multiplier https://www.rabbitmq.com/consumer-prefetch.html

Great Library :)

[actumn]

Thank you for proposal. I will task it in future :)