s/MeasurementPlan/BasicMeasurementPlan/; s/BaseMeasurementPlan/MeasurementPlan/; introduced CompositeMeasurementPlan
test that the rng has not already been used
when calling create_wfa(), use the actual RNG that was passed to the function
we can now pass an RNG to MetropolisSimulation
we now pass a WalkPlan to MetropolisSimulation's constructor, not the actual Walk