First implementation of minimal Broker API

1. Agreed in the sense that I agree in general with the pattern. Right now, I'm not sure yet to it right away or later when needed.
2. Though I'm not fully understanding your point or concerns here, I'm still wondering how receiving a message w/o handling it gives you anything. This in my view is also a 'misuse' of the API if this is possible to do so.
3. I wouldn't worry about the overhead at this stage, unless reality starts proofing us wrong. In general, I also agree having less functions in a class helps for understanding and proper usage. But only one function also seems quite radical in my opinion, as it could mean you don't want more than the constructor :)