[feature] programmatic way to enquire about available instances

[davidschlangen]

For future use as provider of synthetic learning data, it might be useful to provide a way to interact with the collection of games programmatically, without needing to know where the underlying material (game code, instances) live.

For example, make a call to cli.py to find out which games are available, with information like "difficulty level", "amount of feedback", etc. Then, make call to find out which instances are available for a specific game. This could then be used in a meta-loop, where a learner systematically repeats the same instance, trying out different action options (that is, builds a game tree); eventually looping through all instances.

I think we're going in this direction already with the game registry, but this would require surfacing more information, I think.