Produce and send events messages

Summarising our discussion earlier:

In websockets mode, we need to send the events at times that reflect their randomised timestamps. So if we have state messages at times 1000 and 2000, and we generate an event X with timestamp 1432 and an event Y with timestamp 1951, event X should be sent to the websocket around ~432 ms after the previous state, and event Y should be sent around ~951 ms after (and around 500 ms after event X).
Because events are generated while generating the next state (for example, we generate a "close connection" event in the generation of the state where the connection already has the new status), in each iteration, we should store and send the previous state instead of the current one. For example, our events X and Y above would be generated while generating the state at time 2000 (unless we do a complex and unnecessary refactor).
So, the simplest way to achieve this would be something like this, in each iteration:
- Generate the events and state
- Send the events wrapped in something like a timeout for the difference between their timestamp and that of the previous state
- Send the previous state from the previous iteration (if there is one, i.e. this isn't the first iteration)
- Store the new state, to send it next iteration. We should only ever need one previous state stored in memory like this (e.g. let previousState defined before the setInteral loop)

In file / stdout mode, all we should need to do is append the events to the buffer list before appending the new state.

libp2p / observer-toolkit