What would really helpful is a one-page user guide where you explain the Messenger API. I want to know e.g. how to use the different QoS exactly-once, at-most-once, at-least-once and all that stuff I can do with that API without jumping from one header file to another and need to ask questions in mailing lists. Provide basic samples with snippets in the different supported language bindings.
I think Messenger API is quite comparable with SwiftMQ's AMQP 1.0 Client. This is how our client is documented:
That's it. Doesn't took much effort to create it.
Proton is the standard AMQP 1.0 driver. It would be a shame if users went frustrated away from it because they don't understand the basic concepts.