improvements

src/board.rs

@@ -264,6 +264,10 @@ impl Board {
         .count()
     }
 
+    pub fn net_score(&self, piece: Piece) -> isize {
+        self.count(piece) as isize - self.count(!piece) as isize
+    }
+
     /// Returns (White score, Black score)
     pub fn get_score(&self) -> (usize, usize) {
         (self.count(Piece::White), self.count(Piece::Black))