More element index array methods
I noticed that for rendering, we will probably need a few more index array methods. Probably, we will eventually need all of them:
vertex_vertex_indices (n_vertices, max_vertex_valence), vv_indices
vertex_face_indices (n_vertices, max_vertex_valence), vf_indices
vertex_edge_indices (n_vertices, max_vertex_valence), ve_indices
vertex_outgoing_halfedge_indices (n_vertices, max_vertex_valence), voh_indices
vertex_incoming_halfedge_indices (n_vertices, max_vertex_valence), vih_indices
face_vertex_indices (n_faces, max_face_valence), fv_indices
face_face_indices (n_faces, max_face_valence), ff_indices
face_edge_indices (n_faces, max_face_valence), fe_indices
face_halfedge_indices (n_faces, max_face_valence), fh_indices
edge_vertex_indices (n_edges, 2), ev_indices
edge_face_indices (n_edges, 2), ef_indices
edge_halfedge_indices (n_edges, 2), eh_indices
halfedge_to_vertex_indices (n_halfedges,), htv_indices
halfedge_from_vertex_indices (n_halfedges,), hfv_indices
halfedge_face_indices (n_halfedges,), hf_indices
halfedge_edge_indices (n_halfedges,), he_indices