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 RANDOM DESIGN IDEAS extracted from Convex_hull.h
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- Use a policy tag to choose for incremental with inserts only or
  incremental with  removals and inserts.
  In the first case: use Triangulation for storage.
  In the second case: use Delaunay !
    In this second case, we must keeps the points that are inserted in the hull,
    as they may become part of the boundary later on, when some points are removed.
- Constructor with range argument uses quickhull.