Keep procedure

  DECLARATION:  Keep(ExitCode : Word);

      PURPOSE:  Terminates the program and keeps it in memory

         UNIT:  DOS

      REMARKS:  Keep (or Terminate and Stay Resident) keeps the entire
                program in memory, including the stack segment, data segment
                and the heap.  Be sure to use the $M compiler directive to
                specify a maximum size for the heap.  The ExitCode used with
                Keep corresponds to the Halt exit codes.