Function interpolator

interpolator(
colours: Colourish[],
opts?: Partial<ColourInterpolationOpts>,
): (amt: number) => string
Returns a function to interpolate between colours
```
const i = interpolator([`orange`, `yellow`, `red`]);

// Get a random colour on the above spectrum
i(Math.random());
```
Results will vary depending on the colour space used, play with the options. When using a hue-based colour space, the hue option sets the logic for how hue values wrap.
```
interpolator([`orange`, `yellow`, `red`], { space: `hsl`, hue: `longer })
```
Parameters
- colours: Colourish[]
  Colours to interpolate between
- opts: Partial<ColourInterpolationOpts> = {}
  Options for interpolation
Returns (amt: number) => string