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

examples/tower_server.rs

@@ -1,10 +1,11 @@
 #![deny(warnings)]
 
-use hyper::{Body, Request, Response, Server};
-use tower_service::Service;
-use futures_util::future;
 use std::task::{Context, Poll};
 
+use futures_util::future;
+use hyper::{Body, Request, Response, Server};
+use hyper::service::Service;
+
 const ROOT: &'static str = "/";
 
 #[derive(Debug)]