Create design for Instrumentation API

[fabianishere]

For the first public release, we need a design for an Instrumentation API which is able to measure data from the system in simulation and process the data that has been measured.

Goals

• Allow user to measure data from the system in simulation
• Allow user to transform the measured data
• Allow user to use the data (save/store)

Design

• Measurement
  The measurement of data happens in an Instrument, which is similar to a Process and has access to the state of all entities in the model. These measurements can happen periodically, by making the instrument hold (sleep) between the measurements. The measurements are then emitted via the methods provided by the SendChannel interface.

val entity = ...
val instrument: Instrument<Int, Model> = {
    while(true) {
        send(entity.state.counter)
        hold(10)
    }
}

• Installation
  The Kernel interface will provide a method install(instrument: Instrument<T, M>): ReceiveChannel<T> that allows a user to install an instrument into a (running) system. The method will return a stream of measurements of type T (we use ReceiveChannel from kotlinx-coroutines to represent a stream).
• Transformation and Collection
  The idea is to use the channel returned by the install method to asynchronously transform the measurements into meaningful data:

val stream: ReceiveChannel<Int> = kernel.install(instrument)
val avg: Deferred<Int> = async(Confined) { stream.take(100).average() }

kernel.run(1000)