The core improvement is that `Rocket::launch()` now resolves to
`Ok(Rocket<Ignite>)` on nominal shutdown. Furthermore, shutdown never
terminates the running process.
Other changes directly related to shutdown:
* Runtime worker thread names are now irrelevant to graceful shutdown.
* `ErrorKind::Runtime` was removed; `ErrorKind::Shutdown` was added.
* The `force` config value is only read from the default provider.
* If `force`, Rocket's constructed async runtime is terminated.
Other related changes:
* The exported `hyper` module docs properly reflect public re-exports.
* Update 'tokio', 'tokio-rustls', and 'hyper'.
* Remove unused dependencies on some `futures-*` crates.
* Rework 'spawn_on', which is now 'serve'.
* Simplify Ctrl-C handling.
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.
Sergio Benitez
Jeb Rosen
Paolo Barbolini
Marc Schreiber