Basic modules

Close #3 (closed).

• Implement logger. I will need to read up a bit to decide whether it should be mutable or not. It definitely should store messages in JSON and be general enough to handle any events that can be converted to JSON. Should also pretty print logs in human-readable form. Finally, it is probably a good idea to print the log in real time instead of running the whole thing and printing the log only afterwards. But the run_simulation function should definitely return a log as its result. Should the log be typed?
• Implement the scheduler, that is, the run_simulation function. It should not be hard, but it'll definitely take time.

Tests can be added in a separate PR.