Release 10.4.0

[arckoor]

PRs merged:

• algorithms: expose AlgorithmFamily #466
• security: zeroize encoding and decoding keys #483
• Fix formatting in Ed25519 key serialization #485
• Small fixes #498
• Fixup typo in the DecodingKey::from_ec_der method #501
• Fix more clippy complaints #503
• Update changelog for 10.4.0 #507

Pretty much all further PRs break something, so are going to be 11.x.
@Keats can you do a release?