Add previously computed PPSD results to current PPSD instance.
Load previously computed PPSD results from a compressed numpy binary in npz format, written with write_npz() and add the information to the current PPSD instance. Before adding the data it is checked if the data was computed with the same settings, then any time periods that are not yet covered are added to the current PPSD (a warning is emitted if any segments are omitted).
Parameters: filename (str) Name of numpy .npz file(s) with stored PPSD data. Wildcards are possible and will be expanded using glob.glob().