Handle piecewise interpolation using easing functions t_in => t_out with t_out outside [0, 1] range

[danburzo]

For example,

let culori = require("culori");
let BezierEasing = require('bezier-easing');

const easing = BezierEasing(0.425, -0.165, 0.350, 1.465);
const colors = culori.samples(20).map(
  culori.interpolate([easing, '#ff0000', '#cc8833', '#3344cc'])
).map(culori.formatRgb);

console.log(colors);

colors contains NaNs because the Bézier easing produces values outside the expected range.

[danburzo]

Fixed in d75f9bf