function hsl(hue, saturation, lightness){
  if (1 == arguments.length) {
    utils.assertColor(hue, 'color');
    return hue.hsla;
  } else {
    return hsla(
        hue
      , saturation
      , lightness
      , new nodes.Unit(1));
  }
}
Convert the given `color` to an `HSLA` node,
or h,s,l component values.

Examples:

   hsl(10, 50, 30)
   // => HSLA

   hsl(#ffcc00)
   // => HSLA

@param {Unit|HSLA|RGBA} hue
@param {Unit} saturation
@param {Unit} lightness
@return {HSLA}
@api public