To the submenu of MAP with path PATH, add ITEM.
If an item with the same name is already present in this submenu,
then ITEM replaces it. Otherwise, ITEM is added to this submenu.
In the latter case, ITEM is normally added at the end of the submenu.
However, if BEFORE is a string and there is an item in the submenu
with that name, then ITEM is added before that item.
MAP should normally be a keymap; nil stands for the local menu-bar keymap.
It can also be a symbol, which has earlier been used as the first
argument in a call to `easy-menu-define', or the value of such a symbol.
PATH is a list of strings for locating the submenu where ITEM is to be
added. If PATH is nil, MAP itself is used. Otherwise, the first
element should be the name of a submenu directly under MAP. This
submenu is then traversed recursively with the remaining elements of PATH.
ITEM is either defined as in `easy-menu-define' or a non-nil value returned
by `easy-menu-item-present-p' or `easy-menu-remove-item' or a menu defined earlier by `easy-menu-define' or `easy-menu-create-menu'.