Add support for RabbitMQ's E2E Binding Extension

Added bind/unbind support to the Exchange object, allowing it to harness RabbitMQ's "Exchange to Exchange Bindings" (or E2E). See http://www.rabbitmq.com/e2e.html for additional information on this AMQP extension.

I've included documentation updates (for two new Exchange methods), two new tests (for exchange binding and unbinding), etc. Let me know if there's something more needed.