Changes regarding code quality and attempts at improving performance.

Even though I've tried to use core.memoize (not core.cache, as I've stupidly mentioned in my last post) to improve the performance of `get-flippable-points`, it seemed to not do much difference.

What I've tried was something like that:

    (defn get-flippable-pieces- [...] ...)

    (def get-flippable-pieces (memo/fifo get-flippable-pieces :fifo/threshold 128))

Of course in extreme cases (for example greedy v greedy) the gain was more significant.

Overall, the improvement in the speed of execution was negligible (I've tried bumping threshold up to much a higher number).