Abandoned implementation of streaming twirps

This repo contains code implementing a streaming twirp protocol that is no longer part of the twirp roadmap — see twitchtv/twirp#70 for an enlightening discussion and eventual explanation of why support for streaming endpoints was never adopted by the twirp project. For all the reasons raised toward the end of that conversation, this repo is no longer under development and is only still around to serve as a reference for that issue.