Rename Client::request -> send_request (#98)

All other fns have a send prefix.

tests/client_request.rs

@@ -48,7 +48,7 @@ fn recv_invalid_server_stream_id() {
         .unwrap();
 
     info!("sending request");
-    let stream = h2.request(request, true).unwrap();
+    let stream = h2.send_request(request, true).unwrap();
 
     // The connection errors
     assert!(h2.wait().is_err());