Stopping the server (revisit #139)

[Diggsey]

In #139 , there's a suggestion to use loop { server.poll() }. However, this is much more CPU-wasteful than calling server.run(), and I think there are several things rouille could do to make this easier.

• Server::poll_timeout. The underlying server provides the recv_timeout method, so it would be very easy to add this: using even a small timeout means the CPU usage will be much lower than calling poll in a loop.

• Server::handle. This would return a Send + Clone handle which has a method to shutdown the server. This could be implemented by closing the underlying socket, triggering a wake-up, or by setting a flag and then initiating a dummy connection.

[LPGhatguy]

Another approach for this would be to let Server accept an mpsc::Receiver as a shutdown signal, letting the user give the other half of the channel to whatever wants to shut the server down.

This is the approach that Hyper uses, but with a futures::sync::oneshot::channel pair instead of an std::sync::mpsc::channel pair.