code: func (b *Board) MarshalText() (text []byte, err error) {
  	return []byte(b.String()), nil
  }
docs: // MarshalText implements the encoding.TextMarshaler interface and returns
  // a string in the FEN board format: rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR