Update manual bandstop filter to use scipy.butter #41
Description
bandpass_filter(), lowpass_filter(), etc. all use scipy.signal.butter(band="...") . However, the bandstop_filter() doesn't directly use the scipy.signal.butter(btype="bandstop") option. Instead, it manually combines a lowpass and highpass filter.
I assume this is because it was implemented before scipy had a bandstop option? Similarly, bandpass_filter() uses btype="band" rather than bandpass, which again I guess is because when it was implemented scipy only had bandpass as an option and called it just band.
We should update both of these to directly use the correct options in scipy.signal.butter().