new: createMonoSegment, newMonoChain
removed: check_trapezoids_segment_orientation
refactored: appendVertexEntry
renamed: monoDiag -> monoDone
cleanups: removal of reverse links to aid garbage collection
segment elements: all attributes initialized
initMonoChains: creates mono chains in normed winding order
appendVertexOutsegEntry: inlined
splitPolygonChain: removed code handling wrong winding order
test_splitPolygonChain4_CW: activated by testing for wrong results