mplex gets a new flag `is_shutdown` to keep track of when `shutdown` has
been called. We need to make certain that after the shutdown no more
`Sink::poll_complete` or `Sink::start_send` calls are being made which
may result in a panic.
Update the `StreamMuxer` trait.
- `read_substream`, `write_substream` and `flush_substream` now return `Poll` instead of `Result`.
- A new `Shutdown` enum allows for half-closing of substreams and is used in `shutdown_substream`.
- `close_inbound` and `close_outbound` have been merged into `shutdown` which takes a `Shutdown` parameter to allow closing only one direction.
- Add a new `flush_all` method to allow flushing after a series of actions (e.g. multiple `shutdown_substream`).
W.r.t. flushing the general idea is that normal use drains buffers over time. Shutting down a substream does not imply flushing, so can be followed by `flush_substream` or (if multiple substreams are to be shut down) a single `flush_all`. Shutting down the muxer itself proceeds likewise, i.e. `shutdown` followed by `flush_all`.
* Rewrite the swarm
* Small improvement to Debug of ListenersStream
* Fix Swarm::Replaced never being produced
* Fix logic problem when reaching a node in swarm
* Small comment in swarm
* Add closed_multiaddr to Replaced event
* Add address to NodeClosed and NodeError
* Fix concerns
* Remove StreamMuxer::boxed
Retain all incoming buffer elements with different substream ID or equal
Endpoint. The latter was previously not considered which could result in
the removal of data for another substream with same ID but opposite
Endpoint.
* Stronger typing for the swarm handler future
* The swarm future is now a swarm stream of events
* Rewrite StreamMuxer in core
* Update libp2p_mplex for the new stream muxer
* Update yamux for new stream muxer
