Time series moving average

Add simple moving average test to check if time series is drifting.

There are more sophisticated tests for time series behaviour, but they are quite complicated and possibly overkill here.

Actually I am not sure if the wrapping of the boolean return value is handled correctly in line 236 of file _action_cpp.pyx.
Do you guys have an expert opinion on that?
sorry, that's exactly what you're doing.  I didn't read carefully enough