Change behaviour of detrend process

Summary

Change behaviour of detrend process

Current behaviour/setbacks

Detrend process currently:

1. Normalises the time series by dividing it by the mean time series.
2. Compute a moving average according to a window size.
3. Divide the normalised time series by the moving average.

Normalising by dividing by the mean time series is difficult to justify -- it's more likely that a signal's trend is additive to the phenomenon of interest, rather than multiplicative.

Desired behaviour/advantages

Remove normalising by dividing by the mean (step 1). For step 3, subtract time series by the moving average (rather than dividing).

Implementation sketch

Should be straightforward.