This should be a temporary fork of Math-Clipper with early support for points
with Z values. This is a new compile-time option introduced in 
Clipper 6.0.0 alpha.

Ideally Math::Clipper::WithZ should be a minimal XS module that just supplements
Math::Clipper, and not a complete copy. The goal is to develop it in that
direction.

Until that's accomplished (and after), the WithZ fork should work the same as 
Math::Clipper, just with the extra Z feature, and initially a different version
of Clipper under the hood.