Unify chaining and nesting of dataProcessors
The behaviour of dataProcessors is a bit inconsistent. Some support further processing for each object/record they produce (nesting), others support using data from outside the 'data' array (chaining).
For "nesting" it should only be documented that each record/object that is generated is further processed by applying the sub-dataProcessing setting.For "chaining" a new property of each setting that is meant to configure the input data is introduced:
source : can have the values
- "data": read property with the given name from the data array
- "field": read property with the given name from outside the data array
- "value": literal value, no property name