Documentation of rsp_clean() seems inconsistent with implementation

[danibene]

Hello! I am a bit confused about the default method for cleaning respiration signals.

In the docstring, it is written that there is linear detrending followed by a 5th order lowpass Butterworth filter with a cutoff of 2Hz: https://github.com/neuropsychology/NeuroKit/blob/3d004b4777c3e59b288f46b9f0f812ac1e04b5d4/neurokit2/rsp/rsp_clean.py#L18-L19

But the implementation seems to just be a 2nd order bandpass Butterworth filter with cutoffs of 0.5 Hz and 3 Hz: https://github.com/neuropsychology/NeuroKit/blob/3d004b4777c3e59b288f46b9f0f812ac1e04b5d4/neurokit2/rsp/rsp_clean.py#L121-L143

Also, in the cited paper, Khodadad et al. (2018) wrote "However, further improvement is also obtained by pre-processing the data using a digital high-pass filter to remove the dominating low frequency contents. Here, a second order high-pass Butterworth filter has been used with a cut-off frequency of 15 breaths/min." Wouldn't that correspond to 0.25 Hz?

Should we update the documentation to reflect that it is a 2nd order bandpass Butterworth filter with cutoffs of 0.5 Hz and 3 Hz?