Coloraide

- **NEW**: Use `NaN` to track undefined hues.
- **NEW**: Remove `is_hue_null` and add new API function `is_nan` to test if any channel is currently set to `NaN`.
- **NEW**: Remove `get_default` from the `Color` class and instead allow properties that can be overridden when
subclassing the `Color` object.

- **FIX**: Color object API was missing the ability to receive the `premultiplied` argument.

- **NEW**: Expose access to `srgb-linear` color space. This is mainly for development and testing and not listed in docs currently.
- **FIX**: Cylindrical spaces, when calling `overlay` can now request to be overlaid in a different space. This is because alpha composition does not work well in cylindrical spaces. HSL, HSV, and HWB will now request `overlay` to be done in sRGB, and LCH will request overlay to be done in LAB.
- **FIX**: Add support for premultiplied alpha when interpolating via `premultiplied` option.

- **NEW**: Initial alpha release. Library is experimental and API is unstable.