avutil/color_utils: Add basic transfer functions for each AVColorTransferCharacteristic

Most functions are valid over a domain and range of [0.0-1.0] but
some are defined over greater. This patch does not deal with
AVColorRange and assumes AVCOL_RANGE_JPEG for the returned values.

Signed-off-by: Kevin Wheatley <kevin.j.wheatley@gmail.com>
