- Rewrite get_cluster. [done]
- Use Compute_area_2 with three points instead of a triangle. [done]

- Implement a method to split all clusters at the beginnning.

- Histograms in the demo

- do not use default constructor of Geom_traits

- Rewrite Double_map.h [!]

- draw() called twice in mesh_demo [!]

Before CGAL-3.1:

- Update the hierachy if CDT is a CT_plus_2. [DELAYED]
- [doc] concept CDT.
- [doc] pictures [DONE]
- [doc] document Compute_area_2 in a concept. It is used in 
  Delaunay_mesh_criteria_2.
- Fix clusters bug: the algorithm should ignore the Shewchuck rule when 
  inserting point in a *big* triangle. [DONE]