unionRoundSimple

[OpenSCAD issue #844](https://github.com/openscad/openscad/issues/884#issuecomment-898877935)
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#####Easy to understand version but with less safety checks.
#####/ improved smarter rounding

#####With an exploit of fast convex + convex minkowski and the Theorem: Given any collection of convex sets, their intersection is itself a convex set.
#####The following became possible:
```
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/*
unionRound() Module by Torleif Ceder - TLC123 late summer 2021
Pretty fast Union with radius, But limited to a subset of cases
Usage
unionRound( radius , detail , epsilon )
{
YourObject();
YourObject();
}
limitations:
0. Only really fast when boolean operands are convex,
Minkowski is fast in that case.
1. Boolean operands may be concave but can only touch
in a single convex area
2. Radius is of elliptic