Design Straume.Channel

# Why?

- Channels are almost streams
- The language that we use to talk about streams is sufficient to talk about channels (namely, we have logical clocks anyway for pos)
- Channels are important both for implementing actors within the perimeter *and* message passing a la ZMQ outside the perimeter

# What?

- Benchmarking against applicability for implementation of websocket protocol, define:
- [ ] a class for Channels
- [ ] an API for addressing Channels
- [ ] an API for placing message into a queue, respecting the logical clocks if needed
- [ ] an API for consuming messages

The issue names no files, tests, or entry points. Start by reviewing the existing stream concepts and the websocket applicability mentioned in the issue, then define the Channel class, addressing API, message-queue API, and consumption API. Done means all four checklist items are specified and implemented with benchmarking against websocket use.

Written by the indexing model from the issue text.