I wanted to make it a boolean but then I saw that `bias` was an int so I assumed that for some reason numpy preferred to use 0/1 switches instead of False/True. I also put this new kwarg last so it would not interfere with existing calls to this function that assume the current order. I will send an email to the list asking for more input and ideas. If `repeat_weights` is True then the elements of weights must be integers for the results to make sense. The weights are in general not integer frequencies though and in that case we only have the biased covariance. Maybe there are better names for this argument... `frequency_weights`?