HSV colorspace support.

[phoe]

I have a usecase where I want to perform hue rotation on images. This requires that the image is converted into HSV colorspace, which I couldn't find in opticl yet.

[slyrus]

Patches welcome! :)

[phoe]

Yep - as soon as I have some time, I'll happily contribute, perhaps cannibalizing some code from https://github.com/wmannis/simple-rgb or https://github.com/privet-kitty/dufy . I put this issue here mostly so I don't forget.

[slyrus]

@phoe It's a little complicated to use as you need the hsv-image branch of opticl and opticl-core, and the example code is opticl-more-test (on the hsv-image branch) but I was able to rotate the hue in the example and convert to/from 8-bit-rgb-image.