The binary PGM and PPM formats store 16-bit samples most significant
byte first. The decoder and encoder read and wrote them in native
little-endian order, so every wide sample was byte swapped. This
corrects the swizzled colors reported for 16-bit PPM images.
- Reverse the sample byte order in BinaryDecoder and BinaryEncoder.
- Fix integer division in the max pixel value upscale factor.
- Add exact-value, reference-decoder, upscale, and round-trip tests.
- Add a 16-bit PPM test image and its Magick-anchored reference PNG.
- Document the binary decoder and encoder in full.
James Jackson-South
8ca712019e