Marching Squares Algorithm

Ludwig generates the energy contours for its Fermi-surface centered meshes using a simple marching squares algorithm. The implementation is inspired by the implementation in Contour.jl, but modified so that the generated contours are angle-ordered in the first quadrant on either side of the umklapp surface. The marching squares algorithm stores the resulting contours in the convenient Isoline Bundle which stores information about the size and topology of the Fermi surface.