Feature request: allow YAML for all files or implement a loader hook

[Farnsi]

For some parts you use already js-yaml, why not add an option to parse yaml files instead json? The yaml files could then internally be transformed to json and parsed like json.

I think a fork to implement this feature is too much. A loader hook would be a good thing too.

Currently i use a script to read all yaml files, transform them to json, write them to a temp dir where jsonschema2md can use it.