This adds a new test helper library that depends on LittleCMS 2.
For starters, the library implements conversion from enum transfer_fn to
ICC multiProcessingElements compatible LittleCMS curve object.
That conversion allows encoding transfer funtions in ICC files and
LittleCMS pipelines with full float32 precision instead of forcing a
conversion to a 1D LUT which for power-type curves is surprisingly
imprecise.
This also adds CI tests to make sure the conversion matches our
hand-coded transfer functions.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
