Move join_room and leave_room to muc::room module

xmpp/src/muc/mod.rs

@@ -0,0 +1,7 @@
+// Copyright (c) 2023 xmpp-rs contributors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+pub mod room;