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/service/new_service.rs

@@ -3,7 +3,7 @@ use std::error::Error as StdError;
 use futures::{Future, IntoFuture};
 
 use body::Payload;
-use super::Service;
+use super::{MakeService, Service};
 
 /// An asynchronous constructor of `Service`s.
 pub trait NewService {
@@ -47,9 +47,24 @@ where
     type Future = R::Future;
     type InitError = R::Error;
 
-
     fn new_service(&self) -> Self::Future {
         (*self)().into_future()
     }
 }
 
+impl<N, Ctx> MakeService<Ctx> for N
+where
+    N: NewService,
+{
+    type ReqBody = N::ReqBody;
+    type ResBody = N::ResBody;
+    type Error = N::Error;
+    type Service = N::Service;
+    type Future = N::Future;
+    type MakeError = N::InitError;
+
+    fn make_service(&mut self, _: Ctx) -> Self::Future {
+        self.new_service()
+    }
+}
+