feat(service): rename Service to HttpService, re-export tower::Service`

The only important trait for a user is the `tower::Service` trait, which
is now available also at `hyper::service::Service`. The other "trait
aliases" are no longer publicly exported, as people thought they had to
implement them.

Also removes dependency on `tower-make`, which is trivial but otherwise
shouldn't affect anyone.

Closes #1959

src/service/http.rs

@@ -0,0 +1,58 @@
+use std::error::Error as StdError;
+
+use crate::body::Payload;
+use crate::common::{Future, Poll, task};
+use crate::{Request, Response};
+
+/// An asynchronous function from `Request` to `Response`.
+pub trait HttpService<ReqBody>: sealed::Sealed<ReqBody> {
+    /// The `Payload` body of the `http::Response`.
+    type ResBody: Payload;
+
+    /// The error type that can occur within this `Service`.
+    ///
+    /// Note: Returning an `Error` to a hyper server will cause the connection
+    /// to be abruptly aborted. In most cases, it is better to return a `Response`
+    /// with a 4xx or 5xx status code.
+    type Error: Into<Box<dyn StdError + Send + Sync>>;
+
+    /// The `Future` returned by this `Service`.
+    type Future: Future<Output=Result<Response<Self::ResBody>, Self::Error>>;
+
+    #[doc(hidden)]
+    fn poll_ready(&mut self, cx: &mut task::Context<'_>) -> Poll<Result<(), Self::Error>>;
+
+    #[doc(hidden)]
+    fn call(&mut self, req: Request<ReqBody>) -> Self::Future;
+}
+
+impl<T, B1, B2> HttpService<B1> for T
+where 
+    T: tower_service::Service<Request<B1>, Response = Response<B2>>,
+    B2: Payload,
+    T::Error: Into<Box<dyn StdError + Send + Sync>>,
+{
+    type ResBody = B2;
+
+    type Error = T::Error;
+    type Future = T::Future;
+
+    fn poll_ready(&mut self, cx: &mut task::Context<'_>) -> Poll<Result<(), Self::Error>> {
+        tower_service::Service::poll_ready(self, cx)
+    }
+
+    fn call(&mut self, req: Request<B1>) -> Self::Future {
+        tower_service::Service::call(self, req)
+    }
+}
+
+impl<T, B1, B2> sealed::Sealed<B1> for T 
+where 
+    T: tower_service::Service<Request<B1>, Response = Response<B2>>,
+    B2: Payload,
+{}
+
+mod sealed {
+    pub trait Sealed<T> {}
+}
+