producing better shortest path estimate than the "closest next neighbor"
heuristics. The new greedy algorithm utilizes KD tree for closest
end point search, and builds a graph to detect loops.
PerimeterGenerator newly uses the optimized TSP algorithm.
ExtrusionEntity has been refactored / simplified.
Iterator loops replaced with C++11 loops.
Fixed clone() methods to return an ExtrusionEntity*.
PerimeterGenerator now uses move semantics on ExtrusionEntity a little
bit more.
