Changes to bin_1D function
--------------------------

Earlier the bin_1D function if the nx(number of bins) is None
    (if nx is None)

from ::

  nx = core._defaults["bins"]

to::

  nx = int(max_x - min_x)

  Note:
    min_x : float, optional
        Left edge of first bin defaults to minimum value of x
    max_x : float, optional
        Right edge of last bin defaults to maximum value of x