This will allow us to generate code that handle and provide easy access
to metadata stored in TIFF's tags. The generator is a Python script, and
it output both TIFFMetadata.h and TIFFTagHandler.cpp files.
The generator will definitely need some update to support all TIFF and
EXIF tags, but that will still be easier than writing everything
ourselves.
Some small modifications are needed in TIFFLoader.cpp to make it
compatible with the new `Metadata` class.
The differencing predictor is a different way to encode pixels in TIFF
images. Every pixel is encoded as a difference with the previous column
of the image, except the first column, obviously.
This parameter is materialized by a new tag for which reading was also
implemented.
