added undying sound packages support (file versions 79, 80, 81, 83,
and 85: there are additional dwords before the object size index
whose purpose are unknown for now. information found in UT package
delphi library by A. Cordero Balcazar.) documented the header change
beginning with file_version 68. made load_upkg() to dump the header
before returning upon errors. made load_upkg() to check for negative
count or offset header members and error out if found any. added web
link references.