Coloraide

- **FIX**: Address two divide by zero cases in HSL algorithm. Was missing some special cases when luminance equals `1` or `0`.

> **Warning**: _Breaking Change_
> Custom gamut mapping plugins no longer return coordinates and require the method to update the passed in color.

- **NEW**: Improved, faster gamut mapping algorithm.
- **NEW**: FIT plugins (gamut mapping) no longer return coordinates but should modify the color passed in.
- **NEW**: Expose default interpolation space as a class variable that can be controlled when creating a custom class
via class inheritance.
- **NEW**: Colors can now directly specify the ∆E method that is used when interpolating color steps and using
`max_delta_e` via the new `delta_e` argument. If the `delta_e` parameter is omitted, the color object's default ∆E
method will be used.
- **NEW**: Oklab is now the default interpolation color space.
- **NEW**: Interpolation will now avoid fitting colors that are out of gamut unless the color space cannot represent
out of gamut colors. Currently, all of the RGB colors (`srgb`, `display-p3`, etc.) all support extended ranges, but
the HSL, HWB, and HSV color models for `srgb` (including spaces such as `okhsl` and `okhsv`) do not support extended
ranges and will still be gamut mapped.
- **FIX**: Remove some incorrect code from the gamut mapping algorithm that would shortcut the mapping to reduce chroma
to zero.

> **Warning**: *Breaking Change*
>
> The use of `xyz` as the color space name has been changed in favor of `xyz-d65`. This better matches the CSS
> specification. As we are still in a prerelease state, we have not provided any backwards compatibility.
>
> CSS color input strings in the form `!css-color color(xyz x y z)` will continue to be accepted as CSS will allow
> both the `xyz` and the `xyz-d65` identifier, but output serialization will prefer the
> `!css-color color(xyz-d65 x y z)` form as using `xyz` is an alias for `xyz-d65`.
>
> Again, this breaking change only affects operations where the color space "name" is used in the API to specify usage
> of a specific color space in order to create a color, convert, mutate, interpolate, etc.
>
> python
> Color('red').convert('xyz') Bad
> Color('red').convert('xyz-d65') Okay
>
> Color('xyz' [0, 0, 0]) Bad
> Color('xyz-d65' [0, 0, 0]) Okay
>
> Color('red').interpolate('green', space='xyz') Bad
> Color('red').interpolate('green', space='xyz-d65') Okay
>
> No changes to CSS inputs
> Color('color(xyz 0 0 0)') Okay
> Color('color(xyz-d65 0 0 0)') Okay
>

- **NEW**: Custom fit plugin's `fit` method now allows additional `kwargs` in its signature. The API will accept
`kwargs` allowing a custom fit plugin to have configurable parameters. None of the current built-in plugins provide
additional parameters, but this is provided in case it is found useful in the future.
- **NEW**: XYZ D65 space will now be known as `xyz-d65`, not `xyz`. Per the CSS specification, we also ensure XYZ D65
color space serializes as `xyz-d65` instead of the alias `xyz`. CSS input string format will still accept the `xyz`
identifier as this is defined in the CSS specification as an alias for `xyz-d65`, but when serializing a color to a
string, the `xyz-d65` will be used as the preferred form.
- **NEW**: By default, gamut mapping is done with `oklch-chroma` which matches the current CSS specification. If
desired, the old way (`lch-chroma`) can manually be specified or set as the default by subclassing `Color` and setting
`FIT` to `lch-chroma`.
- **FIX**: Ensure the `convert` method's `fit` parameter is typed appropriately and is documented correctly.

- **NEW**: Formally expose `srgb-linear` as a valid color space.
- **NEW**: Distance plugins and gamut mapping plugins now use `classmethod` instead of `staticmethod`. This allows for
inheritance from other classes and the overriding of plugin options included as class members.
- **NEW**: Tweak Lch chroma gamut mapping threshold.
- **FIX**: Issue where it is possible, when generating steps, to cause a shift in midpoint of colors if exceeding the
maximum steps. Ensure that no stops are injected if injecting a stop between every color would exceed the max steps.

- **NEW**: Update spaces such that they provide a single conversion point which simplifies color space API and
centralizes all conversion logic allowing us to pull chromatic adaptation out of spaces.
- **NEW**: `color()` output format never uses percent when serializing, but will optionally accept percent as input.
- **NEW**: Slight refactor of color space, delta E, and gamut mapping plugins. All now specify there name via the
property `NAME` instead of methods `space()` for color spaces and `name()` for other plugins.
- **NEW**: Restructure source structure by flattening out some directories and better organizing source files. This
changes some import paths.
- **NEW**: Color spaces do not specify `alpha` in `CHANNEL_NAMES` as the `alpha` name cannot be changed.
- **NEW**: Color space objects do not need a constant to track number of color channels.

>
>
> If you are working directly in a cylindrical color space and ever wish to force the normalization of color hues
> as undefined when the color meets the usual requirements as specified by the color space's current rules, just
> call `normalize` on the color and it will apply the same logic that occurs during the conversion process.
>
> py
> >>> Color('hsl(270 0% 50%)').normalize()
> color(--hsl none 0 0.5 / 1)
>
> 2. If you relied on commas in CSS forms that did not support them, this behavior is no longer allowed. It was
> thought that CSS may consider allowing comma formats in formats like `hwb()`, etc., and it was considered, but
> ultimately the decision was to avoid adding such support. We've updated our input and output support to reflect
> this. Color spaces can always be subclassed and have this support added back, if desired, but will not be shipped
> as the default anymore.
> 3. The D65 form of Luv and LCHuv is now the only supported Luv based color spaces by default now. D50 Luv and LCHuv
> have been dropped and `luv` and `lchuv` now refers to the D65 version. In most places, the D65 is the most common
> used white space as most monitors are calibrated for this white point. The only reason CIELAB and CIELCH are D50
> by default is that CSS requires it. Anyone interested in using Luv with a different white point can easily
> subclass the current Luv and create a new plugin color space that uses the new white point.
> 4. Renamed DIN99o Lch identifier to the short name of `lch99o`.>

- **NEW**: ColorAide now only ships with the D65 version Luv and LCHuv as D65, in most places is the expected white
space. Now, the identifier `luv` and `lchuv` will refer to the D65 version of the respective color spaces. D50
variants are no longer available by default.
- **NEW**: Add the HSLuv color space.
- **NEW**: DIN99o Lch identifier was renamed from `din99o-lch` to `lch99o`. To use in CSS `color()` form, use
`--lch99o`.
- **NEW**: Refactor chroma reduction/MINDE logic to cut processing time in half. Gamut mapping results remain very
similar.
- **NEW**: Be more strict with CSS inputs and outputs. `hwb()`, `lab()`, `lch()`, `oklab()`, and `oklch()` no longer
support comma string formats.
- **NEW**: Officially drop Python 3.6 support.
- **FIX**: Do not assume user defined, powerless hues as undefined. If they are defined by the user, they should be
respected, even if they have no effect on the current color. This helps to ensure interpolations acts in an
unsurprising way. If a user manually specifies the channel with `none`, then it will be considered undefined, or if
the color goes through a conversion to a space that cannot pick an appropriate hue, they will also be undefined.