implement have message

@kansi while this works correctly to handle chunks and have messages, I am not quite ready to merge this yet -- in particular see 4c686ecbb0f3f1606b21ee547dff7fb2f521f2ea which is sufficient to allow the parser to work while I test it but clearly hardwiring the hash in is not appropriate long-term! I think it makes sense for you to get your peer_worker changes into DEVELOP pretty quickly, and we can use your record for peer state instead of this abomination. Talk to you more about this on Thursday!