CRC校验程序，使用了CRC-16和CRC-CCITT方法 ,CRC inspection program, which use crc-16 and crc-ccitt method

-- crc.vhd -- Used for calculation of CRC16-CCITT -- Intended use is as custom peripheral for Nios processor -- When address is logic 0 => -- Internal CRC register is initialised with write_data value -- When address is logic 1 =>