Modified Julian Date to Gregorian year, month, day, and fraction of a day.
djm double Modified Julian Date (JD-2400000.5)
*iy int year ad *im int month *id int day *fd double fraction of day
-1 = unacceptable date (before 4701BC March 1) The algorithm is derived from that of Hatcher 1984 (QJRAS 25, 53-55). P.T.Wallace Starlink 30 October 1993