Status: going through trailing design iterations, there is enough code to start thinking of making it into a separate tool living in a separate repo.

This is the work that is intended to close #632

This PR is not complete yet, it already works nicely, but I want to improve it more. Almost nothing to review. It's just a draft PR that I'll try to finish as soon as I have time.

TODO

The things to do in this PR:

• (WIP) Complete the specification of deny.schema.yml with the remaining shape of deny.toml configs
• Implement a custom post-processing for the YML schema definition to add a compat crutch for old JSON schema formats that don't support default annotations and enum documentation (not supported in any version)
• Add tests to CI that validate the freshness of the JSON variant of the schema
• Add code generation of markdown documentation for the mdbook. Reseach jsonschema2md for that or write something custom.
• Add code generation for the Rust type definitions from the JSON schema. Maybe we could use some script that does that and then keep the custom deserialization logic that uses toml_span

TODO after merge

Make a PR to the SchemaStore repo with the entry for deny.toml file association.