RSP_Amplitude_Mean is missing from the return values

[michalgnacek]

As of #873
the rsp_intervalrelated no longer returns 'RSP_Amplitude_Mean' as incorrectly indicated by the function description and the documentation.

original code:
if "RSP_Amplitude" in colnames: output["RSP_Amplitude_Mean"] = np.nanmean(data["RSP_Amplitude"].values)

was changed to:
if "RSP_Amplitude" in colnames: rav = rsp_rav(data["RSP_Amplitude"].values, peaks=data) output.update(rav.to_dict(orient="records")[0])

This code seems to be using RSP amplitude to calculate a number of RAV features but the amplitude mean itself is not returned. I thought that perhaps one of the rsp_rav return values is an amplitude mean but from what I understand, RAV_mean and amplitude mean are two different values.

Apologies if I missed something and this is working as intended.