When all Streams are dropped / finished, the Connection was held
open until the peer hangs up. Instead, the Connection should hang up
once it knows that nothing more will be sent.
To fix this, we notify the Connection when a stream is no longer
referenced. On the Connection poll(), we check that there are no
active, held, reset streams or any references to the Streams
and transition to sending a GOAWAY if that is case.
The specific behavior depends on if running as a client or server.
This patch renames a number of types and functions making
the API more consistent.
* `Server` -> `Connection`
* `Client` -> `SendRequest`
* `Respond` -> `SendResponse`.
It also moves the handshake fns off of `Connection` and make
them free fns in the module. And `Connection::builder` is removed
in favor of `Builder::new`.
The Connection type is a `Future` that drives all of the IO of the
client connection.
The Client type is separate, and is used to send requests into the
connection.
This change adds a .rustfmt.toml that includes ALL supported settings,
12 of which we have overridden to attempt to cater to our own
proclivities.
rustfmt is checked in the rust-nightly CI job.
