PHC Wires Art

This is the second version of the wire art for the landing page of the new PHC website.

The first version stored wires as polylines so computing intersections when adding a new wire was O(|number of segments| * |number of segments in whole canvas|) and it got pretty slow after not that much time.

This version instead uses the fact that all segments lie on a grid and can only be of three kinds (going down, down left or down right) and stores them in a "2d integer hashmap" (in js this is just an object indexed by <x>,<y> for example 0,0 or -15,7).

Another improvement is that the screen is redrawn only when considered dirty (the update functions sets this to true after modifying the world state).