YAML schema for .ksy

[GreyCat]

Another suggestion that might be interesting: do a YAML schema to:

1. Make .ksy structure more obvious
2. Allow some validation using standard YAML schema tools, such as kwalify

[GreyCat]

@koczkatamas started JSON schema, which is probably way to go as well: https://github.com/koczkatamas/kaitai_sandbox/blob/master/ksy-json-schema.json

At the very least, we can always trivially convert .ksy YAML→JSON and validate JSON.

[GreyCat]

We've got JSON schema, which seems to be fine and working alternative: https://github.com/kaitai-io/ksy_schema — so I consider this one closed.