MultiAgentEnv interface documentation

[Svalorzen]

I'm trying to inherit MultiAgentEnv to test a custom environment with QMIX (using pymarl); however the documentation for the methods does not specify the types returned by the functions, so I am unsure of what exactly they should return or whether they are all used.

It's also unclear whether all functions need to be implemented, in particular functions that have both a "global" version and an _agent version must be all implemented (for example get_obs and get_obs_agent), but also render etc.

Would it be possible to add some more info on how to extend MultiAgentEnv? A clear example can also work, but in general I guess it's hard to understand from Python code the exact types so I'm not sure whether it would be enough.