Radius map layer with variable distance and user defined color

[grassick]

Create a new layer type that draws a filled circle (buffer actually) a fixed, configurable number of meters around a geometry.

Axis for color, axis for geometry, opacity.

[grassick]

How is ordering of layers done? Does cartocss support z-index? Use attachments for ordering https://www.mapbox.com/tilemill/docs/guides/symbol-drawing-order/