Date and Time routines ("Low Level"):
  Overview        About these routines
  XPstoD()        Convert a YYYYMMDD string to a date variable.
  XPsetDate()     Set the system date
  XPsetTime()     Set the system time
  XPrealDate()    Return the date as stored in the real-time clock
  XPrealTime()    Return the time as stored in the real-time clock
  XPpackDate()    Pack a Date expression into a 2 char sized string
  XPpackTime()    Pack a time variable into a 2 byte sized string.
  XPunpackDate()  Restore the original date from a packed string.
  XPunpackTime()  Restore the time string from packed time
  XPstartTimer()  Start the timer
  XPgetTimer()    Return the elapsed time in seconds.
  XPtimerStr()    Return the elapsed time in a time string