Each getVertices*() method returns a Set\Vertices instance
Add Set\VerticesAggregate Interface + implementation
Add Set\VerticesMap implementation for faster access
Remove unneeded methods getVerticesIds() and getVerticesId()
Add Set\Vertices::getVertexLast() helper
Fix missing imports
Move getting ordering function to helper getCallback()
Add Vertices::getSumCallback() helper
Remove unneeded imports
Throw OutOfBoundsException in Set\Vertices::getIndexVertex()
Remove NO-OP Set\Vertices::ORDER_FIFO
Do not use limited SplPriorityQueue for sorting