* Add listener ID and error event.
Report listener errors to client code so they are aware that an error
occurred within a listener. By default we continue to poll listeners
which produced an error, but clients can remove listeners by ID.
* tcp: Report errors.
Instead of silently waiting after errors we return all errors, but pause
after each error, before continuing.
* Add a test.
To ease testing, `Listener` is made generic and we test that no values
and errors are lost. Elapsed time between item generation is not
measured.
* Support the new methods in core-derive.
* Address review concerns.
* Remove `Display` impl of `ListenerId`.
* Add 'static bound to `on_listener_error` error.
