Imports of xxhsum command

PathSynopsis
fmtPackage fmt implements formatted I/O with functions analogous to C's printf and scanf.
github.com/cespare/xxhash/v2Package xxhash implements the 64-bit variant of xxHash (XXH64) as described at http://cyan4973.github.io/xxHash/.
ioPackage io provides basic interfaces to I/O primitives.
osPackage os provides a platform-independent interface to operating system functionality.