Imports of sign1util command

PathSynopsis
fmtPackage fmt implements formatted I/O with functions analogous to C's printf and scanf.
github.com/Microsoft/hcsshim/internal/cosesign1
github.com/Microsoft/hcsshim/internal/did-x509-resolver
github.com/urfave/cliPackage cli provides a minimal framework for creating and organizing command line Go applications.
osPackage os provides a platform-independent interface to operating system functionality.
stringsPackage strings implements simple functions to manipulate UTF-8 encoded strings.