execute polytree for offsetting

It seems like offsetting in this wrapper can only return a list of polygons and not a polytree.
This is harder to work with when one wants to offset polygons that include holes as matching holes to the correct outer polygon isn't straightforward.

From the Clipper documentation:
http://www.angusj.com/delphi/clipper/documentation/Docs/Units/ClipperLib/Classes/ClipperOffset/Methods/Execute.htm
it looks like Clipper itself supports this. Would there be interest in having this functionality in this wrapper?
Would love to help with implementation but probably need some advice as I've never worked with a C++ wrapper in Julia before.

A bit more information:
The CPP code:
https://github.com/Geri-Borbas/Clipper/blob/master/cpp/clipper.cpp#L3917-L3955

The current Julia part:
https://github.com/JuliaGeometry/Clipper.jl/blob/master/src/Clipper.jl#L278-L285

I don't know what the arguments in ccall are.

Compare the Clipper C++ implementation in clipper.cpp lines 3917-3955 with the Julia wrapper in src/Clipper.jl lines 278-285, focusing on the ccall argument types and return structure. The work is complete when the wrapper can expose offset results as a polytree so polygons with holes retain their outer-polygon association.