[board] Implement a couple handy piece getters

Board::find_pieces returns a BitBoard for all the pieces matching the given Piece.

Board::enemies returns a BitBoard of all the enemy pieces of a given Color.

Board::pawns returns a BitBoard of all the pawns of a given Color.

board/src/board.rs

@@ -63,6 +63,10 @@ impl Board {
         self.pieces.get(square)
     }
 
+    pub fn find_pieces(&self, piece: Piece) -> BitBoard {
+        self.pieces.find_pieces(piece)
+    }
+
     /// Place a piece on the board.
     ///
     /// ## Errors
@@ -102,6 +106,15 @@ impl Board {
     pub fn opposing_occupancy(&self, color: Color) -> BitBoard {
         self.pieces.opposing_occupancy(color)
     }
+
+    pub fn enemies(&self, color: Color) -> BitBoard {
+        self.pieces.opposing_occupancy(color)
+    }
+
+    /// Return a [`BitBoard`] of all pawns of a given color.
+    pub fn pawns(&self, color: Color) -> BitBoard {
+        self.pieces.find_pieces(Piece::pawn(color))
+    }
 }
 
 impl Board {