Changes since 2.20:

o  rc759 diskdef renamed to rc75x, as it works for the series
o  diskdefs.5 added
o  Many disk formats from Larry Kraemer added
o  Renamed ampdsdd to ampro400d for consistency with libdsk and because
   ampdsdd very likely was wrong
o  Check for invalid block size
o  Output line number for diskdefs errors
o  Correctly output create or access time for CP/M 3 in cpmls
o  Spectravideo SVI-728 diskdef added
o  $DESTDIR support
o  Correctly handle empty files
o  Fix block allocation for large directories.
o  Fix time stamp conversion
o  Allow user number 16-31 for CP/M 2.2
o  Intel MDS/22 formats added
o  Crash when using blocksize 16384 fixed
