Switch from AES-GCM to XChaCha20-Poly1305

[matheus23]

• Updated the notation to use Encrypted<> instead of AesGcm<> and KeyWrapped<> instead of AesKw<>. This is more in line with how Hash<> was named.
• Updated the text to refer to a 24 byte IV, and updated the byte threshold per-block to 262,104 bytes.
• Updated the ascii diagram

❗ merge order ❗

1. Update rsa modulus endianess to match most protocols #66
2. Remove namefilter.md and add NameAccumulator verification algorithm #68
3. Specify Blake3's derive_key algorithm instead of SHA3 #69
4. This PR
5. Add baseName to ExternalContent #71

[expede]

A couple minor questions and suggestions, but otherwise looks good :)