Add fromAMQP and toAMQP library adapters

Stream messages to and from AMQP brokers with support for multiple types
of exchanges. Tested with a Ruby publisher, stream parsing in streamtools, and a Ruby consumer on another topic routing key all through RabbitMQ.

This is my first dive into writing in Go, and I appreciate any feedback on changes to make this better.  Also, I apologize for the large formatting difference in `library.go`; the changes are from using `go fmt`.