hsl method Null safety
Creates chalk with foreground color defined from HSL (Hue, Saturation and Lightness) color space parameters. https://en.wikipedia.org/wiki/HSL_and_HSV
Implementation
Chalk hsl(num hue, num saturation, num lightness) {
var rgb = ColorUtils.hsl2rgb(hue, saturation, lightness);
return makeRGBChalk(rgb[0], rgb[1], rgb[2]);
}