Feature request: Support combining of CRC64-NVME checksums.

[pauldoo]

Hello,
This is a request that "combining" CRC64-NVME checksums be supported. Specifically, please add a function which given the CRC64 of byte stream A, the CRC64 of byte stream B, and the length of B, will return the CRC64 of A concatenated with B.

Example of this function being supported by the crc32c crate: https://docs.rs/crc32c/0.6.8/crc32c/fn.crc32c_combine.html