- For release:
  * add example that demonstrates how to get edge info
  * remove enumeration type Arrangement_type as an enum type and add small
    is_*() methods that query the type
  * add test suites for {insert,remove}_degree_2 in TDS_2
  * add test suites for join_vertices & split_vertex in TDS_2
  * customize traits with predefined kernels, as well as add something
    in the doc for that

- add hierarchy specific tests in the hierarchy test suite
- make sure that the assignment operator and copy constructor for the
  segment Voronoi diagram hierarchy class do not have any bugs
- in predicates/Svd_arrangement_type_C2.h put all functions inside the class
- add a method insert_point_no_search in the segment Voronoi diagram class
  that inserts a point without searching for the nearest neighbor;
  the assumption here is that the nearest neighbor given is already known
  and we do not need to search again; the insert_point method should be 
  rewritten so that it uses insert_point_no_search as a subroutine; the
  segment Voronoi diagram hierarchy needs this method when inserting a point:
  the nearest neighbors of the point at all levels are known...
- use the input sites container as the container where point handles
  are gotten from
- in class Svd_basic_constructions_C2.h, inside method to_ft, check
  if sqrt is supported by the number type; actually this is ok for predicates
  but constructions also need to use this too.
- add the methods insert_polyline and insert_polygon that do some
  optimized insertion for polylines and polygons; add these in both
  the one-level and hierarchy classes
- add/document method that takes two vertex handles corresponding to
  input points and adds the segment that connects them
- add test program for hierarchy with the two data sets that have overlapping
  segments
- add test suite for info (new design using storage traits)
- add examples that use the info
- add a demo that uses the red-blue info stuff; the demo should
  automatically color the segments/points
- rename file names to match the names of the classes they contain