Added support for encrypting multiple files at once :partying_face:

This allows to remove the awkward find ... -exec staticrypt ... - we can now just do staticrypt foo.html bar.html directory/* to encrypt multiple files or a whole folder. This allows things to be neatly organized: you can now have a decrypted/ folder and an encrypted/ folder, and upload your encrypted/ folder wherever.

By default directories aren't opened recursively, you need to add the -r flag for that.