[structure] separate framework from benchmark (from games?) / make pip installable

[davidschlangen]

Separate (in the repository) the code for the clemgame framework, and for the games.

Besides being more aesthetically pleasing, this would also make it possible to make the framework pip installable.

What needs to be discussed is if further divisions would be possible. One could imagine that even games that are part of the benchmark need not live in the same repository. ... Actually, maybe not. While there can of course be games that live in their own repository (and cli.py should be able to run them), it would probably be too much of a hassle to ensure consistent runs of the benchmark if the code for the constituent games would need to come from several repositories.

So, just two repositories: one for the framework (with everything that's needed to make it pip installable), one for the benchmark.

[Gnurro]

I think it's too early to split things up - mainly due to the fact that the games side of clembench is not much of a framework, at least to me. I expect a framework to handle clearly defined specifications (in this case of games) in a concise format, which do not have or need arbitrary code. Currently almost every clemgame does things very differently in terms of code, and there's no clear way to how to do even that, not to mention any unified way to define clemgames.