Add support for json-schema

[vkottler]

http://json-schema.org/

This is maybe more generic than https://docs.python-cerberus.org/en/stable/index.html ?

[vkottler]

https://en.m.wikipedia.org/wiki/Microdata_(HTML)

some interesting things you can do in HTML, plus https://schema.org/docs/gs.html

trying to figure out what all "schema languages" there are

Maybe "Color" has a schema.org schema?

[vkottler]

We should add schemas for the setup.cfg data and pyproject.toml data for vkottler/vmklib#18

so we should decide if this kind of improvement cuts in or not

[vkottler]

e.g. the JSON schema for PEP 518: https://peps.python.org/pep-0518/#json-schema

[vkottler]

https://json-schema.org/understanding-json-schema/UnderstandingJSONSchema.pdf

https://json-schema.org/understanding-json-schema/index.html

need to read through these

[vkottler]

Well, I guess we also need #60, and that's probably easier than ripping out / adding some kind of secondary backend for schema parsing (since we're pretty hard-coded for Cerberus)

[vkottler]

Maybe it would be possible to detect if a schema is meant to be read as Cerberus or JSON schema?

[vkottler]

Let's do vkottler/workspace#6 first and refactor some of the generic code in this package, out

[vkottler]

https://datatracker.ietf.org/doc/html/rfc6901#section-3

[vkottler]

We may want to do this now that we're working on vkottler/rcmpy#1