Create unit test framework for mini-protocol message CBOR encoding/decoding

[agaffney]

We need to be able to test that all of the mini-protocol message objects decode as expected from known CBOR and that an "identical" message object created from scratch properly encodes back into the same CBOR. We know that many of them will not for now, so we just want to create the framework and implement a few simple messages in each mini-protocol.