feat(server): keep-alive!

Internals have been shuffled around such that Request and Reponse are
now given only a mutable reference to the stream, instead of being
allowed to consume it. This allows the server to re-use the streams if
keep-alive is true.

A task pool is used, and the number of the threads can currently be
adjusted by using the `listen_threads()` method on Server.

[breaking-change]

benches/client.rs

@@ -7,28 +7,25 @@ extern crate test;
 
 use std::fmt::{mod, Show};
 use std::io::net::ip::Ipv4Addr;
-use hyper::server::{Incoming, Server};
+use hyper::server::{Request, Response, Server};
 
 fn listen() -> hyper::server::Listening {
     let server = Server::http(Ipv4Addr(127, 0, 0, 1), 0);
     server.listen(handle).unwrap()
 }
 
-macro_rules! try_continue(
+macro_rules! try_return(
     ($e:expr) => {{
         match $e {
             Ok(v) => v,
-            Err(..) => continue
+            Err(..) => return
         }
     }})
 
-fn handle(mut incoming: Incoming) {
-    for conn in incoming {
-        let (_, res) = try_continue!(conn.open());
-        let mut res = try_continue!(res.start());
-        try_continue!(res.write(b"Benchmarking hyper vs others!"))
-        try_continue!(res.end());
-    }
+fn handle(_: Request, res: Response) {
+    let mut res = try_return!(res.start());
+    try_return!(res.write(b"Benchmarking hyper vs others!"))
+    try_return!(res.end());
 }