Add or enhance a function to extract JSON-Records from an JSON-API

[TobiasNx]

While we are able to extract JSON records which are arrayed at the top level in an JSON file we are not able to extract JSON records from an JSON API that has the records in an array in an (sub-)field. At the moment we can't extract or split the records. The JSON file received via the JSON-API is extracted as one record:

"https://imoox.at/mooc/local/moochubs/classes/webservice.php"
| open-http(accept="application/json")
| as-lines //as-records has the same result
| decode-json
...

Example for file:
https://imoox.at/mooc/local/moochubs/classes/webservice.php

In the field "data" there are the JSON records as objects. These objects should each be retrieved as single records.

Functional Review: @TobiasNx
Code Review: @dr0i

[blackwinter]

I guess something like a RecordPathFilter would be actually nice to have. More or less a generic version of org.metafacture.xml.XmlElementSplitter. Maybe based on XPath or JSONPath?

...
| decode-json
| filter-records-by-path("$.data")
...

[fsteeg]

Implemented with a JSON path as suggested by @blackwinter, but as an option in JsonDecoder, because we have the full JSON to query the JSON path against at that point: db8f5a1

[TobiasNx]

Hei, it works fine for that +1 Cool that this worked out so fast.

In my opinion the function code needs some documentation about the options/attributes that can be selected.
For a new user this is not very instructive.

[fsteeg]

Assigned and requested review from @dr0i in #384, unassigning myself here.