YAML support

Hey @josdejong!

First off, I am a HUGE fan of this package, and I use it every chance I get :)

For example:
https://oas-def-gen.lukehagar.com

I am curious if YAML language support is possible for this package.

The example above is a good one to show why I would love yaml language support in this editor, the right-hand side of this page swaps between yaml and JSON output, and it would be cool to use this editor on the right as well.

But even further than that I want to build out an editor for OpenAPI Specifications, and the tree-style functionality you have for JSON is PERFECT for the tool I want to build out in YAML.