Recompute ridge_points and ridge_vertices after making regions finite

[alonfnt]

Currently, making regions finite only changes voronoi.regions and voronoi.vertices. If we were to update the ridges too, then our resulting BoundedVoronoi object would also be compatible with scipy's voronoi_plot_2d, as well being more consistent.

It only requires to do some bookkeeping at BoundedVoronoi._make_regions_finite() to add the new ridges.

The boundary ridges, which are composed of 2 elements from the bounding polygon, may include the same point twice (inner Voronoi node) to avoid the infinite trick on the plotting function.

Suggestions are welcome.