inside ClipperUtils are now using bit shifts instead of multiplication
by doubles, which makes the scaling precise.
Removed the scale parameter from all offset functions.
Modified the safety offset to calculate offset per polygon instead
of over all polygons at once. The old way was not safe and very slow,
sometimes this meant a kiss of death for supports for example.
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.
