Support userdata pass-through into JSON about hypertest

[mchlrch]

Note that the current implementation is very simple and requires the text block to begin with a comma, in order to get valid JSON generated. This will probably change later on.

[tpluscode]

Actually, I think we should revert this.

The syntax is awkward, likely going to cause more harm than good.

This is meant to be used during the development of the DSL itself, in order to try out concepts that are not yet part of the proper grammar.

It will be sufficient to work with the JSON itself when prototyping new structures for the DSL, without the need to maintain a feature we don't really want