Swap moves

[tewalds]

• Store whether you can swap in Board
• in AgentMCTS::Node::value: if(swap) val = min(val, 1-val); before adding knowledge to find the move closest to 50%
• in AgentMCTS::return_move:
  • if first move, return as normal, search found closest to 50%
  • if second move, return as normal if best move > 50%, otherwise swap.
• change History to always copy the baseboard to maintain the rules
  • change Board constructor (not copy constructor) to output the board rules to stderr?