paration method should be employed
       ('Lyne_Hollick','UKIH'), default = 'UKIH'
   parameters: specify filter parameters ([filter_parameter nr_passes] for 
       Lyne Hollick, default = [0.925 3]; [n_days] for UKIH, default = 5)
   plot_results: whether to plot results, default = false

   OUTPUT
   BFI: baseflow index [-]
   error_flag: 0 (no error), 1 (warning), 2 (error in data check), 3
       (error in signature calculation)
   error_str: string contraining error description
   fig_handles: figure