rate iterator test

[klucar]

dividing by the time difference between two samples while calculating the rate of a time series is the correct way. Since we have the filter iterator, it would be interesting to see how dividing by the time compares to doing a moving average rate calculation using the vector: {-0.154303, -0.308607, -0.617213, 0.617213, 0.308607, 0.154303}