Age

[george-angel]

Allow Strongbox to use age https://github.com/FiloSottile/age primitives for encrypting files.

This allows users to use .strongbox_recipient files in the Git repository for encryption and ~/.strongbox_identity to store identities for decryption.

age encryption has feature parity with SIV and a few nice extras:

• fix the known issue with file ordering when decrypting
• allow multiple recipients
• compatible with age outside of Git workflow
• offloading encryption, compression and decoration to an external (and a very good) library

age encryption is in addition to the current SIV encryption and remains backward compatible.