Ultimate Bushing Collection-rounded, flanged, plain, customizable

The creates bushings with smooth, rounded-over edges. They might be useful as drillguides, adapters, plugs, washers, playing pieces, tokens, etc...

Depending on the facets set by $fn, the outer diameter circumscribes the corners, while the inside/hole diameter is inscribes the internal sides. So the generated shapes will fit inside a hole of the chosen diameter, while a shaft of the hole diameter will fit in in the low-side count bushings.

Set the hole diameter to 0 to produce a slug.
Set the Flange Thickness > 0 to produce a flange.

The math gets weird if the breaks and undercuts interfere with the diameters, so avoid that.

This is a rework of https://www.thingiverse.com/thing:5577366 using the rounding ideas of https://www.thingiverse.com/thing:6009075 instead of the Round Anything library from https://github.com/Irev-Dev/Round-Anything so it should work in the old thingiverse customizer.