EMGroupReadReceipt 成员列表

成员的完整列表，这些成员属于 EMGroupReadReceipt,包括所有继承而来的类成员

	from	EMGroupReadReceipt
	messageId	EMGroupReadReceipt
	readCount	EMGroupReadReceipt
	readReceiptId	EMGroupReadReceipt
	timestamp	EMGroupReadReceipt