code: function(curve, location, distance) {
  		var p = _pointAlongPath(curve, location, distance);
  		if (p.location > 1) p.location = 1;
  		if (p.location < 0) p.location = 0;
  		return _gradientAtPoint(curve, p.location);
  	}
docs: returns the gradient of the curve at the point which is 'distance' from the given location.
  if this point is greater than location 1, the gradient at location 1 is returned.
  if this point is less than location 0, the gradient at location 0 is returned.