CLI interface

[KapJI]

Because no standard tool can unpack encrypted archives locally, it'd be really great to have a basic CLI interface which can:

1. Unpack all files from the archive, allowing to use plaintext password and take care about converting password to key (like superviser does).
2. Pack files, with gzip or without, encrypted or not.
3. Detect if gzip should be used based on file extension.
4. Maybe specify buffer size as well.

I can put some PR if you're happy with that.

[pvizeli]

work for me, feel free to create a PR for that