Unify the interface of Hypermap
libvb/Toroidal: choose a vertex of highest degree as the origin
libvb/Toroidal: add point markers for initial vertices and edges
2d/Belyi_Torus: make number of subdivisions customizable
libvb/Toroidal: closer to the ACPA paper, fewer moving parts
libvb/Hypermap: also learn to remove vertices/faces of degree 1