Array output value processing

[Fydar]

The RPGCore prototype allowed for an array output to be consumed by a single-object input and for the Instance to be instantiated multiple times for each of the elements in the array output.

In the rewrite, this will be accomplished with sub-graphs. A node will contain a sub-graph and the sub-graphs inputs can reference outputs defined outside of the sub-graph.

Sub-graphing should be nestable.

The Unity Editor implementation might be the hardest part of the implementation of this feature.

Sub-graphing will also be useful for creating selector-graphs to evaluate the elements in a collection to filter out elements or select only a few of them.