Fixed medianBin not working according to it's docstring

As it stands medianBin creates bins with medianWidth + 1 elements in them, instead of medianWidth elements, as specified in the docstring (if I understand it correctly that is).

I'm not sure if rounding up numberBins is the right thing to do, as this can make the last bin have even just one element. On the other hand rounding it down would make it miss few datapoints in certain cases.