Curvy edgemarks for Penrose pipes

[gordonwoodhull]

I copied the cube grid to get started with the Penrose grid, and so this grid inherited pointy edge marks:

It would be much nicer for the edge marks to be curvy like the pipes, and there are at least two ways to do this:

• Using SVG's stroke-dasharray
• By doing the math to split the splines

It will have the same effect either way. stroke-dasharray will be less code and probably easier; perhaps pathLength can be set to draw the edgemark as a portion of the total length of the pipe spline.