improve player management

src/main.rs

@@ -1,11 +1,12 @@
 use agent::QueueAgent;
 use game::Game;
-use repr::Piece;
+use piece::Piece;
 
 mod agent;
+mod board;
 mod game;
 mod misc;
-mod repr;
+mod piece;
 
 fn main() {
     let player1 = QueueAgent::new(