unionRound module

OpenSCAD
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unionRound Module by Torleif Ceder - TLC123 late summer 2021
Pretty fast Union with radius, But limited to subset of cases
Usage
```
unionRound( radius , detail , epsilon= 0.00001)
{
YourObject1 ();
YourObject2 ();
YourIsolatingMASKObject ();
}
```

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 type and is only approximate r were operand intersect at perpendicular angle.
3. For chamfer detail can be set to 1 with approximate double the radius

```
module unionRound(
radius=1, // fillet radius
detail=5, // fillet detail
epsilon = 0.00001, // some numeric CGAL issues resolve with dif