feat(server): change NewService to MakeService with connection context

This adjusts the way `Service`s are created for a `hyper::Server`. The
`MakeService` trait allows receiving an argument when creating a
`Service`. The implementation for `hyper::Server` expects to pass a
reference to the accepted transport (so, `&Incoming::Item`). The user
can inspect the transport before making a `Service`.

In practice, this allows for things like getting the remote socket
address, or the TLS certification, or similar.

To prevent a breaking change, there is a blanket implementation of
`MakeService` for any `NewService`. Besides implementing `MakeService`
directly, there is also added `hyper::service::make_service_fn`.

Closes #1650

src/server/tcp.rs

@@ -8,7 +8,7 @@ use tokio_reactor::Handle;
 use tokio_tcp::TcpListener;
 use tokio_timer::Delay;
 
-use self::addr_stream::AddrStream;
+pub use self::addr_stream::AddrStream;
 
 /// A stream of connections from binding to an address.
 #[must_use = "streams do nothing unless polled"]
@@ -194,6 +194,7 @@ mod addr_stream {
     use tokio_io::{AsyncRead, AsyncWrite};
 
 
+    /// A transport returned yieled by `AddrIncoming`.
     #[derive(Debug)]
     pub struct AddrStream {
         inner: TcpStream,