update palette to 0.6

[subpop]

Updates palette to 0.6 in the dependency list in Cargo.toml and ports
colors.rs to the 0.6 conversion changes.

Fixes: #115

[ids1024]

This seems to result in the same hue and saturation numbers displaying a somewhat different color than before.

I'm not entirely sure if that's purely an issue with this PR, or if the code is already kind of wrong in how it handles sRGB vs linear RGB. Or I guess palette was also doing things wrong from this quite in the 0.6 release notes:

They were previously only linear, due to an incorrect assumption, resulting in some situations where they could not give the same result as in other graphics software.

Dealing with linear and non-linear RGB seems to be surprisingly hard to get right and something software often messes up...

[subpop]

Yea, palette definitely change the way it handles linear RGB. I opened a discussion on the palette discussions while I was trying to figure out how to port this to palette 0.6. Converting to linear is now an explicit additional method call. I am not deeply familiar with how these color encodings work. From my somewhat limited use of the LED coloring on my launch_1, the colors look "the same".