Revise connect_point_erosion().

Include inner as well as outer anchor points (inners are removed if they result in endpoints).
Replace likelihood map with a simple product of the normalized travel depth and (new) mean curvature maps.
Add incremental output vtk files for debugging.
Add segmentation at each iteration, and remove a fraction of the lowest values per segment.
Test for simple topology ignores the second output of topo_test().