Create a JSON Schema for every new version

[tomootes]

Currently we have the JSON-Schema at schemastore.org. For many purposes, like the publiccode.yml-editors that exist, it would be handy if we could use the JSON Schema of a specific version. Currently we can only link to this current version: https://github.com/SchemaStore/schemastore/blob/master/src/schemas/json/publiccode.json. It's not even pinned so i expect it to change when a new version gets rolled uit.

I would like to create a new JSON Schema for every new version. We can use this to validate publiccode.yml files and approach it as the single source of truth.

Imo this also removes the need for parser projects like https://github.com/italia/publiccode-parser-go/issues. It could simply be replaced by a generic tool which works with JSON Schema's. This eliminates a lot of work.

[bfabio]

Hey @tomootes that would be nice but see #304 (comment).

It'd require we use some sort of format that can represent all the contraints. Protobuf? I'm not actually sure. Also maybe it's even more work than do it by hand every new release.

I agree we should have a JSON schema for each major release. Keep in mind minors are backward compatible and you can use that schema for every v0 (which should be renamed to publiccode.v0.json or something).