#30 rename, add and delete folders

[bakalite]

It would be very useful to be able to call a number of
functions or methods that do the following:

1) Rename a menu item
2) Add a menu item
3) Delete a menu item

I'm using the menu tree as a folder list where all
documents within a folder appear in a seperate frame,
much like many email clients.

Being able to simply manipulate the menu structure
within the items array would be very useful, permitting a
user to make changes without a visible frame refresh.

Updating the underlying menu structure could occur
elsewhere entirely.