Basic tic-tac-toe without AI
Added class TicTacToeNode with #initialize and #children (potential states)
Added marks as constants in module. Also created 'mark' attribute for Player class. General refactoring as well.
Added to class TicTacToeNode the following methods: #losing_node?(player), #winning_node?(player), #players_turn?(player), #any_winning_children?(player), #any_losing_children?(player)
Finished. Fixed bug related to calculating the status of the board each time a move is made, and record the winner only the first time we see one (just in case). Also, added method Board#over? which returns true if we have a winner or if the board is filled. Also, added a stop early for losing nodes, as there was a bug that was getting past the first winner (the reason why I noted the precaution stated at the beginning was necessary); with the stop early, I stop as soon as the game is over (Board#over?) and if Board#won? is not true (tie) it is a non losing node, but if it's true, I check if the winner is the opponent in order to classify the node