Wrote another G code generator function.

Given x and y of the cone center axis, z of the bottom and top, top
and bottom radius, and a few other parameters like finish quality, I
can mill out a vertical cone. I first rough it out quickly, and then
mill the inner surface to desired quality.

It seems to work. I am watching it right now on the webcam, sitting in
the family room. The finishing process with ball mill is tedious, I
set the finishing step to 0.01 inch.

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