3 Strand Braided Ring (OpenSCAD)

This is [sauer's 3 Strand Braided Ring](https://www.thingiverse.com/thing:2053823/) ported to OpenSCAD.


sauer's formula for the braid:
```
r(t) = ringRadi + ellipseWidth + ellipseWidth * sin(periods * 2 * t)
θ(t) = t
z(t) = ellipseHeight * fudgeFactor * pow(cos(t * periods/2), 2)
```

Ring prints best with no infill, one perimeter, and zero top and bottom layers.