Implement an oracle validator for Jelly

[Ostrzyciel]

It would be nice if the Jelly test kit (#25) included an oracle for validating Jelly data. The oracle could be a very technical but simple implementation Jelly with code annotations referring to specific pieces of the spec. It would have extensive error handling with very descriptive messages.

It could then also be used as a validator for Jelly data in general. This would be useful in development, but also in debugging deployed systems.

[Ostrzyciel]

It may be better to just make a general CLI utility for working with Jelly. Could be based on Jelly-JVM, with AOT compilation for fast startup.

Functionalities:

• Validate Jelly-RDF, Jelly-Patch... anything else that will pop up in the future
• Mock gRPC consumer and producer
• Convert Jelly-RDF/Patch/whatever to/from W3C-standard formats
• Convert binary protos to the Protobuf Text Format

[Ostrzyciel]

I started a repo for this: https://github.com/Jelly-RDF/cli

I'll create follow-up issues there.