[FEATURE] Create Sub-Circuits via Code

[SvarunSoda]

Instead of creating a sub-circuit by building it in the simulator and using the Create Subcircuit menu button, is it possible to program a sub-circuit as a Java or JavaScript code file, and somehow loading that into the simulator?

So, instead of the sub-circuit's behaviour being dictated by its circuit components, its behaviour would be defined by its code.

Would something like that be possible to do in the current version of the simulator? I'm assuming it would not be possible using the UI, but would there be an alternate way of doing it?