Use JSON Canonicalization Scheme (JCS)

[joepio]

Although the tests are currently passing, and most commits seem to work just fine, I'm pretty sure that there will be situations where the deterministic json-ad serialization will be different from the Typescript version.

To prevent this, I should switch to serde_jcs. Also, double check in atomic-data-browser that this spec is used as well.

Also https://docs.rs/serde_canonical_json/latest/serde_canonical_json/

[joepio]

Also, maybe use JSON Web Signature encoding? https://crates.io/crates/jws

See atomicdata-dev/atomic-data-docs#35

[joepio]

Also, don't use base64 in URLs (because of =, / characters), maybe consider base64URL

[joepio]

I used serde_canonical_json. Not sure it is actually JCS, though: gelvinp/rs-serde_canonical_json#1

EDIT: switched to serde_jcs because the other one wasnt JCS.