Added skcms_AreApproximateInverses(Curve, TransferFunction)

Centralizes our roundtrip error calculation, and adds
functions to get three transfer functions: sRGB, sRGB^-1, I.

Change-Id: I3c2cb5d0eed2245d5436b80072982bc623b2ed74
Reviewed-on: https://skia-review.googlesource.com/128881
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
38 files changed