The coefficient generation is not precise enough :/ The associated low pass filter is quite different that the scipy version
Refactored how butter worth coefficients are computed. Should put the common pieces somewhere else like IIR
Put zpk common functions inside IIR
Fixed the new generation and start adding band pass implementation
Added band pass tests -> failing for the moment
Fixed a stupid mistake on delays

Band pass tests OK
Added band stop filter
Merge branch 'feature/ButterworthGenericFilters' into develop