add dialog for audio settings, flesh it out

not functional yet tho

src/libui_sdl/DlgAudioSettings.h

@@ -0,0 +1,29 @@
+/*
+    Copyright 2016-2019 StapleButter
+
+    This file is part of melonDS.
+
+    melonDS is free software: you can redistribute it and/or modify it under
+    the terms of the GNU General Public License as published by the Free
+    Software Foundation, either version 3 of the License, or (at your option)
+    any later version.
+
+    melonDS is distributed in the hope that it will be useful, but WITHOUT ANY
+    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+    FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with melonDS. If not, see http://www.gnu.org/licenses/.
+*/
+
+#ifndef DLGAUDIOSETTINGS_H
+#define DLGAUDIOSETTINGS_H
+
+namespace DlgAudioSettings
+{
+
+void Open();
+
+}
+
+#endif // DLGAUDIOSETTINGS_H