jsonschema

I’m not convinced json schema is very mature (had some flakey
experiences with libraries), but since we probably need to do this at
some point, I added the start of a json schema for the CSL input
model.

https://github.com/citation-style-language/schema/blob/master/csl-data.json

It’s more-or-less a skeleton at this point as I’m busy with other
things. But perhaps we can use that as a target around which to
formalize and stabilize the model over time?

The priority here is something that maps cleanly to the CSL internal
model. But if it can be useful to other projects, that’d be great too.

Feel free to fork away if you like.

Bruce