Add from/to websocket adapters

Add a websocket module:

* `fromWebSocket` - create a stream containing all messages received on the supplied websocket.  If a websocket error occurs, the stream fails with the same error.  When the websocket closes, the stream ends.
* `toWebSocket` - send all events from the supplied stream to the supplied websocket.  If the websocket closes *or* errors, the stream will end or error, respectively.  If the stream ends or errors (via a prior `takeUntil`, for example), it will stop sending additional events to the websocket.

Simple example client/server included.  Still needs:

- [ ] JSdoc
- [ ] Unit tests