feat(server): support HTTP1 and HTTP2 automatically

If an HTTP/1 connection has a parse error, but it starts with the HTTP2 preface, converts the connection automatically into an HTTP2 server connection.

Closes #1486

src/proto/h1/dispatch.rs

@@ -332,6 +332,9 @@ impl<S> Server<S> where S: Service {
             service: service,
         }
     }
+    pub fn into_service(self) -> S {
+        self.service
+    }
 }
 
 impl<S, Bs> Dispatch for Server<S>