Initial release

This release provides a basic and functioning client. However, there are still several TODOs in our list:

1. Embed the commit hash into the binaries for the version command to work.
2. Offer password-based encryption of files under ~/.utok.
3. Add debugging capabilities based on log/slog.
4. Fix the use of generics when refreezing tokens.
5. Some more stuff we're forgetting for sure...