feat(ssl): redesign SSL usage

BREAKING CHANGE: Server::https was changed to allow any implementation
  of Ssl. Server in general was also changed. HttpConnector no longer
  uses SSL; using HttpsConnector instead.

examples/server.rs

@@ -41,7 +41,7 @@ fn echo(mut req: Request, mut res: Response) {
 
 fn main() {
     env_logger::init().unwrap();
-    let server = Server::http(echo);
-    let _guard = server.listen("127.0.0.1:1337").unwrap();
+    let server = Server::http("127.0.0.1:1337").unwrap();
+    let _guard = server.handle(echo);
     println!("Listening on http://127.0.0.1:1337");
 }