Fetches a menu.
Returns a Promise object or the 'this' object.
Options is a struct that can have the following items, all of which are optional.
Menu-name is a string that is the name of the menu.
Menu-file is a string that is the name of the file containing the menu definition. The default is 'Menus.xml'.
Directory is a relative path to the directory where menu-file is located. Directory is relative to the WebSite directory. The default is '../xml/menus/'.
Promise determines the return value of this function. If promise has the value 'true' (the default), a Promise object is returned. If promise has the value 'false', the ‘this’ object is returned instead.
Success-function is a function called after the operation has successfully completed.
Error-function is a function called if an error occurs.