Began work on logic to creating a boundary line for the map.
Incorporated my save_svg() code, and worked more on the boundary generation.
Got the logic to create a boundary shape mostly working, though it does not
guarantee yet that the final shape is closed.
Boundary line : prevent creating 45 degree angles at end of a quadrant.
Boundary: store edges in a list (do not update the grid yet), and repeat
the process of making a boundary until the final point matches start point.
fixed silly bug
Improved iterate_boundary() logic with a table of possible dirs, and tidied up
a few things...