- Fix building JVM. Previously builds of the JVM succeeded, but Rakubrew
  considered the resulting version as broken.
- Make Rakubrew more resilient to errors resulting from broken versions.
  Previously Rakubrew would error on certain commands if a broken version
  was present.
- Make the `register` command platform independent.
- Add some more testing.
- Make sure the Windows shim wrappers modifying the environment. Previously
  they added a `command` and `brew_cmd` env var.
- Try to reverse the effects of the PAR wrapper on the environment on
  MacOS. Previously on MacOS several env vars were added and
  `DYLD_LIBRARY_PATH` was modified in shim mode on MacOS.
- Switch shims to use `symlink` instead of `link` on *nix. That should
  allow for having the shims on a different partition from the rakubrew
  executable.
