Develop minimax algorithm

Both Caribbean and Code4life winner strategy are based on minimax algo.

https://github.com/Agade09/Agade-Code-4-Life-Postmortem/blob/master/Agade_C4L_Postmortem.md

https://recursive.cc/blog/coders-of-the-carribean-post-mortem.html

TODO :

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

#26

@tyrcho I realized that what you've implemented is actually a negamax algo. Is it right?

Yep, this is the alpha beta optimization of negamax.