WIP: MCTS, alphabeta algorithms for 2p

[tyrcho]

@huiwang sorry for the single commit, I got a weird issue with my laptop and I had to clone again the repository.

MCTS is working well with good performance and several tests. alphabeta still requires quite some work :

• [ ] trim branches from root
• [ ] real game tests (connect4 ? need a game with a working heuristic)
• [ ] performance checks
• [ ] iterative deepening

[huiwang]

@tyrcho do you want to merge this PR first and then transform the todos to other tasks that we can do in the future?

[tyrcho]

Yep, it's OK with me, better not to let branches live too long.