Add support for code snippets in Wax
We want to use Editoria for the upcoming PubSweet documentation Book Sprint Jun 18-20. Before then, we'll need to add support in Wax for code snippets.
This will need to support:
- both inline snippets and whole blocks of code
- a way to specify the language for code blocks (probably not inline), even if Wax doesn't support syntax highlighting (that could wait til export I think).
This one will need some unpacking. As @christos suggests, a good starting point might be to see what the built-in substance code feature already has and go from there.