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/mod.rs

@@ -1,9 +1,9 @@
-//! Services and NewServices
+//! Services and MakeServices
 //!
 //! - A [`Service`](Service) is a trait representing an asynchronous function
 //!   of a request to a response. It's similar to
 //!   `async fn(Request) -> Result<Response, Error>`.
-//! - A [`NewService`](NewService) is a trait creating specific instances of a
+//! - A [`MakeService`](MakeService) is a trait creating specific instances of a
 //!   `Service`.
 //!
 //! These types are conceptually similar to those in
@@ -19,17 +19,21 @@
 //! [`service_fn`](service_fn) and [`service_fn_ok`](service_fn_ok) should be
 //! sufficient for most cases.
 //!
-//! # NewService
+//! # MakeService
 //!
 //! Since a `Service` is bound to a single connection, a [`Server`](::Server)
 //! needs a way to make them as it accepts connections. This is what a
-//! `NewService` does.
+//! `MakeService` does.
 //!
 //! Resources that need to be shared by all `Service`s can be put into a
-//! `NewService`, and then passed to individual `Service`s when `new_service`
+//! `MakeService`, and then passed to individual `Service`s when `make_service`
 //! is called.
+
+mod make_service;
 mod new_service;
 mod service;
 
-pub use self::new_service::{NewService};
+pub use self::make_service::{make_service_fn, MakeService};
+#[doc(hidden)]
+pub use self::new_service::NewService;
 pub use self::service::{service_fn, service_fn_ok, Service};