1) Merged robust_fpt and sqrt_expr_evaluator into voronoi_fpt_kernel;
2) Merged voronoi_output and voronoi_sweepline into voronoi_diagram;
3) Started to use Boost.Polygon point and directed segment types for input and as the output of the voronoi_helper interpolation procedure;
4) Added type traits (not finished yet);
5) Updated tests.
6) Using segment set clean method to remove intersections from the input segment set.
Removed denominator from the circle_event as it's evaluated in a robust way.