Override method signature on quantitiveScale to enable method chaining.
Clean up return type on ordinalScale.domain
Finish the Renderer.projector refactor
(Where by finish I mean it passes unit tests, examples still broken and code not final.)
Instead of having custom xAccessor, yAccessor setters on renderers and other ad hoc methods
there is a Renderer.projector method which takes an attribute to project onto (eg "cx" or "stroke"),
an accessor function to get the perspective out of the data source, and (optionally) a scale to project
the data through.