NegaScout & skip turn

• MegaScout implemented. (Should be faster than mini-max for depth>=4)
• Continue turn rule makes the opponent must skip, instead of keeping a turn. This lead to simpler implementations.

Mini-Max agent

Mini-max agent with alpha-beta pruning is added

Subcommand and Agents

Features

Subcommand

Two modes are supported by subcommand

• play mode
  Play a game with agents
• arena mode
  Compare agents and show win rates

Agents

Three types of AI agents are supported

• Random policy
• Max policy
• Exact pocket policy