- redo the menu a bit, add in some C++ support code to make it a little bit more flexible

- further tweaks. reduce clutter in custom resolution submenu by moving it to another
- add 'prevmenu' ccmd

src/menu/menu.cpp

@@ -853,6 +853,22 @@ void M_ClearMenus()
 //
 //=============================================================================
 
+void M_PreviousMenu()
+{
+	if (CurrentMenu != nullptr)
+	{
+		DMenu* parent = CurrentMenu->mParentMenu;
+		CurrentMenu->Destroy();
+		CurrentMenu = parent;
+	}
+}
+
+//=============================================================================
+//
+//
+//
+//=============================================================================
+
 void M_Init (void) 
 {
 	try
@@ -1032,6 +1048,11 @@ CCMD (closemenu)
 	M_ClearMenus();
 }
 
+CCMD (prevmenu)
+{
+	M_PreviousMenu();
+}
+
 //
 //		Toggle messages on/off
 //