Use I/O traits and types from 'tokio-io' as much as possible.
A few adapters only exist in futures-io-preview and use
futures-tokio-compat as a bridge for now.
Types can now implement the new 'Listener' trait, which means they can
report the address they are listening on and asynchronously accept
connections. 'Connection's are read/write streams that can additionally
report the remote address.
Listener is implemented for 'tokio_net::tcp::TcpListener' and for
the new 'rocket_http::tls::TlsListener' based on 'tokio-rustls'.
The new private function 'Rocket::listen_on()' now does the main setup
for launch and is generic over a Listener. In the future, a more refined
version of the API can be exposed so that applications can implement
their own listeners.
Jeb Rosen
Sergio Benitez