Add more assign algorithms and better search heuristics

[grunt-lucas]

Additional assign algorithms may help. E.g. some kind of A* with a decent heuristic. What else? Can we add better heuristics to the assign algos we already have?

• https://theory.stanford.edu/~amitp/GameProgramming/Heuristics.html
• https://realtimecollisiondetection.net/blog/?p=56

Do more research into heuristics and approximation strategies for solving bin packing, since palette assignment is just a slight variant of this problem. Porytiles currently uses an algorithm known as first fit decreasing, but other bin packing strategies exist which may be worth exploring.