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PackBits Compression Algorithm

The following packing algorithm originated on the Mac, was adopted by
Electronic Arts/Commodore for use in the IFF standard, and then by Tom
Hudson for use in DEGAS Elite.  The algorithm is currently used in
MacPaint, IFF, and DEGAS Elite compressed file formats.  Each scan line
is packed separately, and packing never extends beyond a scan line.

For a given control byte 'n':
    0 <= n <= 127   : use the next n + 1 bytes literally (no repetition).
 -127 <= n <= -1    : use the next byte -n + 1 times.
         n = -128   : no operation, not used.