Imports of 3-build command

PathSynopsis
fmtPackage fmt implements formatted I/O with functions analogous to C's printf and scanf.
github.com/spdx/tools-golang/builderPackage builder is used to create tools-golang data structures for a given directory path's contents, with hashes, etc.
github.com/spdx/tools-golang/tvsaver
osPackage os provides a platform-independent interface to operating system functionality.