Optional epsilon: numberan optional epsilon
an array of array of points, where each point is an array of 2 or 3 numbers
map vertices_coords onto each face's set of vertices, turning each face into an array of points, with an additional step: ensure that each polygon has 0 collinear vertices. this can result in a polygon with fewer vertices than is contained in that polygon's faces_vertices array.
a FOLD object, with vertices_coords, faces_vertices