Implement specification changes from draft-ietf-openpgp-crypto-refresh

[larabr]

The crypto-refresh document is still being drafted (https://datatracker.ietf.org/doc/draft-ietf-openpgp-crypto-refresh/), but we should implement/update the new features before its release.

To update/change:

• AEAD encrypted messages
• AEAD encrypted secret keys (S2K identifier 253)
• V6 secret keys
• V6 signatures
• V6 PKESK and SKESK
• support keys with no User IDs
• use direct-key signatures for reading and writing key expiration, algorithm preferences, etc
• drop support for armoring "multipart" messages
• don't create armor checksum lines
• padding packet
• intended recipient fingerprint (not really new but encouraged by the crypto refresh)
• packet criticality and error handling
• reject invalid MPIs
  ...

To add from scratch:

• Curve448
• Argon2
  ...