All tests pass but some features are still missing/unclear:
- Mesa agents do not have a `state`, so their "metrics" don't get stored. I will
probably refactor this to remove some magic in this regard. This should get rid
of the `_state` dictionary and the setitem/getitem magic.
- Simulation is still different from a runner. So far only Agent and
Environment/Model have been updated.
See CHANGELOG.md for a full list of changes
* Removed nxsim
* Refactored `agents.NetworkAgent` and `agents.BaseAgent`
* Refactored exporters
* Added stats to history
