Show HN: Snebu Backup now supports client side public key encryption

The documentation at https://www.snebu.com needs a bit more of an overhaul, however updated it to reflect how to use the encryption features. Take a look at https://www.snebu.com/tarcrypt.html for a description of how the tar based encryption filter is implemented. Current release of Snebu is 1.1pre1, since this has also had a major refactoring (clean up) of the code. Therefore will need to perform additional volume testing before marking the release as final.