Use hcl instead of hsl?

[hadley]

I noticed that rotate() uses hsl rather than hcl, but my recollection is that hcl is more perceptually uniform, so I think it would be better to use hcl.

I was also surprised see that "HSL" is the default in clr_lighten() — I re-read the colorspace paper to check that I wasn't missing something, but I see:

HLS() (Hue-Lightness-Saturation) is another transformation of (s)RGB that tries to capture the perceptual axes. It does a somewhat better job but the dimensions are still strongly confounded. See Wikipedia (2019f) for more details.