Squircle script

 From:  bemfarmer
Here is an upgrade of the squircle script, "SquircleZ2D," for placing half a squircle between two picked points.
The squircle is drawn in the z axis direction, but may have some portion with an x or y component.

Added in a slider for the shape. The slider does not continously update like the binding "Bulge" one in MoI blend factory, or maybe I've left something out.
(Another version has just numeric entry for the shape value.)

It is required that for the two points, either the x values must not be equal, or that the y values must not be equal. There is some buggy-ness in 3D view,
in the event that respectively, the x values and the y values are each very nearly equal.

I anticipate using the script to place squircles on two guide rails, in Top view, for a sweep.
Checking the repeat box permits many curves to be placed, quickly.

Did some testing with a cube edge skeleton, in 3D view.
Negative heights are allowed.
Used cross product to create an orthogonal axis for a new frame.
Re-used lots of code from many other scripts.
Did not provide for foreign languages "substitution" of name labels..."

Now to go back to the extremely difficult Levenberg-Marquardt solver.