Abbrevdir$ (string)

   Synopsis:
      Returns the abbreviated form of a direction

   Notes:
      The current dictionary stores a number of custom primary, secondary and
         relative directions, in both abbreviated and unabbreviated forms. If
         'string' is stored there, returns the abbreviated form of the
         direction; otherwise, returns 'string' unmodified.
      See also the Unabbrevdir$ () function.
