Added a safe variant of offset(const Slic3r::ExPolygon...), which offsets each loop separately.
New functions "remove_sticks" to remove zero area parts of polygons.
New functions "remove_small" and "remove_degenerate" for polygon clean up.
Extended the C++ supports, those are not finalized yet though.
these regions are grown to anchor the bridge lines to the bottom surface.
The grown regions may overlap. In that case the regions are now merged
before the bridging direction is calculated for the merged region.
