code: func (cr CastleRights) CanCastle(c Color, side Side) bool {
  	char := "k"
  	if side == QueenSide {
  		char = "q"
  	}
  	if c == White {
  		char = strings.ToUpper(char)
  	}
  	return strings.Contains(string(cr), char)
  }
docs: // CanCastle returns true if the given color and side combination
  // can castle, otherwise returns false.