This patch introduces support for handling colr, gama, pasp, and fiel atoms.

These atoms are part of the Video Sample Description Extensions - documented here:
https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap3/qtff3.html#//apple_ref/doc/uid/TP40000939-CH205-124374

To access these atoms, additional handling of ProRes, mjpeg, and DNxHR /DNxHD codecs was added. Other codecs may need similar treatment, but these are the ones I most frequently encounter.

This pull request satisfies my very ancient feature request #167 .

The new functionality was tested via the following workflow:

# Extract an existing colr atom from a qt into a new file 'colr':
mp4extract 'moov/trak/mdia/minf/stbl/stsd/ap4h/colr' input.mov colr

# Or

# Generate a new colr atom from scratch (This one is rec2100 NCL)
echo -n -e '\x00\x00\x00\x12colrnclc\x00\x09\x00\x10\x00\x09\x0a' > colr

# Patch the colr atom from input.mov with the contents of the file 'colr' and write to output.mov
mp4edit --replace 'moov/trak/mdia/minf/stbl/stsd/ap4h/colr':colr input.mov output.mov

I've tried to adhere to the style of the surrounding library, but please let me know if I should change anything.