The client benchmarks did not have to be changed at all for this whole
refactor, and the server benchmark only had to specify a single type parameter,
and only because it writes out the type of Listener, which is not normal
usage.
Adds a benchmark for testing the speed of hyper's server.
Due to limitations of rust-http, `cargo bench` now needs to be
killed after running because there is no way to kill a rust-http
server after you start it.
