Creates a new menu with the given label.
If label contains a &, it is handled specially;
on Windows, the character following a & is underlined in
the displayed menu title to indicate a keyboard mnemonic. Pressing
and releasing the Alt key switches to menu-selection mode in the menu
bar where mnemonic characters are used for navigation. An Alt
combination might select a specific menu via on-menu-char. A && in label is replaced by a
literal (non-navigation) &ersand. On Unix and Mac OS X,
&s in the label are parsed in the same way as for Windows,
but no mnemonic underline is displayed.
If help-string is not #f, the menu has a help
string. See get-help-string for more
procedure is called by the default
method with the object itself.