Causes MarxMenu to exit. If the Bat command is used or batch commands
are used under an OnKey statement then MarxMenu will create a batch file
and set the environment variable MXCMD to point to it. If no batch file
is to be created, and MXCMD hasn't been set to any value then the menu
system will exit by setting MXCMD to MXSTOP.
ExitMenu is normally used without a command. If you use an optional
command with ExitMenu then MarxMenu will run the command and not come
back to the menu.
ExitMenu 'DIR /W'