Change SIZE_RETURN_VALUE to 512

[salix5]

• change SIZE_RETURN_VALUE to 512
• change returns.bvalue to uint8
• update the conclusion in #473

Now The max size of select_cards: UINT8_MAX The max size of cards in response: UINT8_MAX

Cancel in card selection: FF FF FF FF (int -1) Cancel in card sort: FF (unsigned char UINT8_MAX)

@mercury233 @purerosefallen