Creates a context menu
h = uicontextmenu()
// Create a context menu
hMenu = uicontextmenu();
// Create sub menus
hItem1 = `uimenu`_("Label", "Item1", "Parent", hMenu, "Callback", "disp(""Item1 clicked!"")");
hItem2 = `uimenu`_("Label", "Item2", "Parent", hMenu, "Callback", "disp(""Item2 clicked!"")");
hItem3 = `uimenu`_("Label", "Item3", "Parent", hMenu, "Callback", "disp(""Item3 clicked!"")");