Adding a "length" function to scaleLinear (and maybe other continuous scales)

[rben01]

When I have a d3.scaleLinear object, very frequently I'll want to convert the length of some object in domain coordinates into range coordinates. For instance, if an object has a length of x in domain coordinates, then I'd compute its length in range coordinates using scale(x)-scale(0), but this introduces a needless computation of scale(0). It would be nice to have a convenience function scale.length(x), where a scale whose equation is y = a*x+b computes scale.length(x) as simply a*x. This would be useful for shapes like rect and circle that are defined by their dimensions in range coordinates (width, height, r), but which you might want to specify using their dimensions in domain coordinates.

This could probably also be extended to other continuous scales. For instance, a log scale y = m*log(x) + b would treat x as a ratio of two points in the domain and have scale.length(x) == m*log(x).