Creates a new Checksum, using the checksum algorithm
checksum_type is not known, null is returned. A
Checksum can be used to compute the checksum, or digest, of an arbitrary binary blob,
using different hashing algorithms.
A Checksum works by feeding a binary blob through update until there is data to be checked; the digest can then be extracted using get_string, which will return the checksum as a hexadecimal string; or get_digest, which will return a vector of raw bytes. Once either get_string or get_digest have been called on a Checksum, the checksum will be closed and it won't be possible to call update on it anymore.
the desired type of checksum
the newly created Checksum, or null. Use