Add a new example program that demonstrates how to produce a custom USB storage menu and interact with the builtin menu options correctly.
    
    Fix a couple of very minor problems with the other usb storage example.
    
    Deprecate the display message functionality.  The improvements to write recently have oblivated the requirement for these functions.  Plus, they don't play well with the newer library capabilities.
    
    Fix typo in LDoc in menus.
    
    Add USB functions for detecting the existence of files and directories.  They can be used anywhere of course but typically will be used for usb storage devices.
    
    Fix a nasty bug in the usb storage support routines that only permitted 'idle' mode operation.
    
    Rename REMOVE to EJECT.
    
    Add a detection of code change to toggle the reboot after updating via the menu.