Allow independently specifying YAML schema to validate JSON, and vice versa

[stdedos]

It can just so happen that both of the reference documents are on different languages. While it makes no sense, it can happen (e.g. Gitlab CI schema is on JSON, Gitlab CI configuration itself is on YAML).

It'd be really convenient to be able to independently specify the documents' format.

[jdesrosiers]

Yep, that's a good suggestion. I'll look into it when I can.