Remove the concept of individual `Transport::Listener` streams from `Transport`.
Instead the `Transport` is polled directly via `Transport::poll`. The
`Transport` is now responsible for driving its listeners.
A `ProtocolsHandler`, now `ConnectionHandler`, handels a connection, not
a protocol. Thus the name `CONNECTIONHandler` is more appropriate.
Next to the rename of `ProtocolsHandler` this commit renames the `mod
protocols_handler` to `mod handler`. Finally all combinators (e.g.
`ProtocolsHandlerSelect`) are renamed appropriately.
Implement `NetworkBehaviour` on `either::Either<L, R>` where both L
and R both implement `NetworkBehaviour`.
Add NetworkBehaviour derive tests for Either and Toggle
Co-authored-by: Max Inden <mail@max-inden.de>
