This version makes a few significant changes:
- 'add-determinism' is renamed to 'add-det'. A compat symlink should
  be provided in packaging. Only the binary is renamed, the project
  retains the long name.
- 'add-det' was rearchitectured to use threads instead of processes. This
  makes the passing of data between workers simpler. Actually, the only
  places where unsafe code was used was in data sending and receiving over
  sockets. This is now replaced by single-producer-multiple-consumer and
  multiple-producer-single-consumer channels to distribute jobs and gather
  statistics. There is some barely-noticeable improvement in processing
  speed too.
- Compilation is fixed on macOS.
- A new 'linkdupes' program is added for
  https://fedoraproject.org/wiki/Changes/Hardlink_identical_files_in_packages_by_default.
  It seems to work fine, but proper testing hasn't been done yet.
  Also, the program is single-threaded, so slower than it should be.