TODOs in statement template rules section

[garemoko]

TODO: consider allowing limited scripting a la https://github.com/json-path/JsonPath . TODO: consider if use cases require allowing a JSONPath expression to be a union of other JSONPath expressions.

[fugu13]

I've removed the TODO from the text (PR incoming shortly) since we can consider this issue to be replacing it. The second part is already captured elsewhere, so this issue is for the limited scripting possibility.