NIP44 encryption standard, revision 3 (#746)

* Introduce NIP-44 encryption standard

* Finalize NIP-44

* Update spec.

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Co-authored-by: Jonathan Staab <shtaab@gmail.com>

README.md

@@ -24,7 +24,7 @@ They exist to document what may be implemented by [Nostr](https://github.com/nos
 - [NIP-01: Basic protocol flow description](01.md)
 - [NIP-02: Follow List](02.md)
 - [NIP-03: OpenTimestamps Attestations for Events](03.md)
-- [NIP-04: Encrypted Direct Message](04.md)
+- [NIP-04: Encrypted Direct Message](04.md) --- **unrecommended**: deprecated in favor of [NIP-44](44.md)
 - [NIP-05: Mapping Nostr keys to DNS-based internet identifiers](05.md)
 - [NIP-06: Basic key derivation from mnemonic seed phrase](06.md)
 - [NIP-07: `window.nostr` capability for web browsers](07.md)
@@ -52,6 +52,7 @@ They exist to document what may be implemented by [Nostr](https://github.com/nos
 - [NIP-39: External Identities in Profiles](39.md)
 - [NIP-40: Expiration Timestamp](40.md)
 - [NIP-42: Authentication of clients to relays](42.md)
+- [NIP-44: Versioned Encryption](44.md)
 - [NIP-45: Counting results](45.md)
 - [NIP-46: Nostr Connect](46.md)
 - [NIP-47: Wallet Connect](47.md)