Use Maps or WeakMaps instead of Objects for better V8 performance

[Uzlopak]

I think we should implement LookupObject e.g. BaseChannel.consumers as Maps or WeakMaps instead of Objects. V8 creates for each shape of an Object a new V8-Class of that Object. So if you dynamically consume and cancel queues V8 should become slower and slower. If we use Maps it should have not that effect.

[carlhoerberg]

We do this in https://github.com/cloudamqp/amqp-client.js/ already

[cressie176]

published in amqplib@0.9.1 Thank you @Uzlopak