[FIX] Use memcpy instead of sprintf in TarFile::store() for version

* Travis CI gave an error because copying "  " to header.version using
  sprintf would likely (definitely?) NULL-terminate the string,
  overflowing into the next entry in the PosixTarStruct. memcpy should
  just copy the two characters.
[INTERNAL,BUILD] Split PosixTarHeader-based code into seperate files

* This is to address comments on PR #1023 regarding the license of code
  taken from elsewhere that is licensed under Apache 2.
[DOC] Update 3rd-party license file for tarball.*