LIBSLIC3R: Port Support

[lordofhyphens]

Either port prusa3d supports or the mainline Slic3r support generation to C++ for use in CPPGUI.

[Samir55]

@lordofhyphens I will start working on this 😃

[Samir55]

@lordofhyphens I am examining SupportMaterial Class in Prusa3d. I will try to finish porting by 28 June. My work will be in this branch https://github.com/Samir55/Slic3r/tree/supports_porting.

[lordofhyphens]

So just a FYI, there's not much in the way of formal tests for supports in that code that wasn't already in Slic3r.

I'd highly recommend writing tests as you go (I've got Catch up and running on cppgui).

If you're looking for things to write tests against, here's something that should encapsulate what we're looking for. As bugs are found in the code (un-looked for corner cases), we can add more tests and prevent regressions.
https://github.com/slic3r/Slic3r/wiki/Support:-Requirements