Coloraide

- **NEW**: sRGB string output parameter `hex_upper` has been renamed to just `upper`. Expose it in documentation as well.

- **FIX**: More efficient calculation of CIELAB, following CIE 15.3:2004. Results are still the same, but it makes the math a little simpler.
- **FIX**: HSV did not always set hue to `NaN` when saturation was `0`.
- **FIX**: Give better conversion results by having HWB colors pass through HSV instead of sRGB.
- **FIX**: Fix slight issue with REC.2020 and ProPhoto color space conversion. Small issue when using `<=` when `<` was desired.

- **FIX**: More stable saturation calculation for HSL to ensure divide by zero doesn't occur. `2(V - L) / (1 - abs(2 * L - 1))` is likely to yield zero in the denominator when `L` is very small, while the equivalent `(V - L) / min(L, 1 - L)` is not.

- **FIX**: Ensure that when `hex`, `compress`, and `names` is enabled in `to_string` for `srgb` that colors will still match the color name if the color can be compressed.

- **FIX**: Ensure all cases, in regards to gamut mapping, are done the same.