Disabled asserts in the release build (-DNDEBUG).

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.

xs/src/libslic3r/ExPolygon.cpp

@@ -585,4 +585,9 @@ BoundingBox get_extents(const ExPolygons &expolygons)
     return bbox;
 }
 
+bool remove_sticks(ExPolygon &poly)
+{
+    return remove_sticks(poly.contour) || remove_sticks(poly.holes);
+}
+
 } // namespace Slic3r