1) Don't allocate ExtruderOverrides if not necessary
2) Use boost::container::small_vector<int32, 3) for ExtruderOverrides
(usually less than 4 instances are printed))
of the Z coordinate, compiled in the ClipperLib_Z namespace.
Update of Lukas's new brim clipping:
All the brim contours are now clipped by the ClipperLib_Z library
in one shot.
