* Removed references to `set_state`
* Split some functionality from `agents` into separate files (`fsm` and
`network_agents`)
* Rename `neighboring_agents` to `neighbors`
* Delete some spurious functions
See CHANGELOG.md for a full list of changes
* Removed nxsim
* Refactored `agents.NetworkAgent` and `agents.BaseAgent`
* Refactored exporters
* Added stats to history