Trying to default the type parameters leads to an ICE and strange type errors.
I think this is just due to the experimental state of default type params and
this change can be rolled back when they are fixed.
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.
