[FEATURE REQUEST] Hue/Saturation adjustments in ImageBufAlgo

[SergeyShlyaev]

It would be very handy to have function(s) in ImageBufAlgo to adjust hue/saturation of the image. Either all image or some masked region.

Having a case where region filled with fillholes_pushpull() calls needs saturation adjustments. Currently have to do it externally. Would be very handy to do inside of OIIO.

It could be nice to match those operations to similar operations from popular Nuke software from The Foundry. Please take it as suggestion only.

For saturation it would be Saturation node from Nuke with two parameters. Float "Saturation" and enum "luminance math" which is usually set to rec709. For hue it would be HueShift node.

Can also use any other math that helps dialling saturation and changing hue.

Thank you.