starting to refactor aio1 in aio2. looked at norvig's code, no data structure needed, simply need to bubble up terminal utility value
wrote aio2, but there are multiple problems
- runhaskell -XScopedTypeVariables -XFlexibleInstances -XTypeSynonymInstances -XOverlappingInstances aio2
- plays always in lower right corner again
- very slow for empty board, possibly not efficient