Expose d3.scaleSequential?

[mbostock]

It would be nice for implementing custom scales, e.g., the (highly not recommended!) angry rainbow:

var rainbow = d3.scaleSequential(function(t) {
  return d3.hsl(t * 360, 1, 0.5) + "";
});

Instead, you currently must do something like this if you want a scale:

var rainbow = d3.scaleLinear().interpolate(function() {
  return function(t) {
    return d3.hsl(t * 360, 1, 0.5) + "";
  };
});

But note that this doesn’t really work with a domain of more than two values, and ignores the range. So restricting this to a sequential scale seems more appropriate.