Store annotations as metadata

[str4d]

bellman's API design includes namespacing, that strongly encourages circuit developers to annotate their circuits and gadgets with human-readable descriptions indicating the usage of the gadgets within the circuit (e.g. "compute ivk", rather than naming the gadgets themselves like "BLAKE2s").

The zkInterface format supports metadata on both variables and (arrays of) constraints. It would be great for ZkifCS to collect bellman's namespacing data in some format (e.g. some/path/like/string) and then place it into the relevant metadata places.