Default color test / example
Move r2f and friends to Util
Apply style depending on PrimitiveMode of GlPrim, selecting line or fill color as appropriate
Render closed Path elements as a two GlPrims, a LineLoop and a TriangleFan

This of course only works for convex polygons.  For non-convex
polygons it draws the convex hull, and we continue drawing straight
lines across cubic curves.
Example with filled polygons
Interpolate points along cubic curves

For now, arbitrarily pick 30 points along each Cubic element.

Someday, push this interpolation to a tesselation shader (on the GPU),
decide how many points to interpolate based on curvature and final
rendered size.
Example to test / demonstrate curve rendering

For now, just a filled circle.
Add defaultOptions, intermediateRep

Both are aids to debugging, by breaking what defaultMain does into
smaller steps.