add another Math2D.isAnticlockwise()
add SegmentCoordIterator
add Polygon2D.getPointsInHoles()
remove Segment.bisect()
add two generic parameters to Segment
make AbstractSegment a generical implement
extract GeneralLine2D which have 2 generic parameters

  + also restrict Line2D's pred and succ be Line2D only
  + accordingly modify AdaptiveCellEdge which extends Line2D
from Polygon2D, extract GeneralPolygon2D which has 2 generic parameters
add WingedEdge interface and a SimpWingedEdge and a WingedEdgeUtils