old_contents: from .rank import *
  from .percentile_rank import *
  from .bilateral_rank import *
  
new_contents: from .rank import (autolevel, bottomhat, equalize, gradient, maximum, mean,
                     meansubstraction, median, minimum, modal, morph_contr_enh,
                     pop, threshold, tophat, noise_filter, entropy, otsu)
  from .percentile_rank import (percentile_autolevel, percentile_gradient,
                                percentile_mean, percentile_mean_substraction,
                                percentile_morph_contr_enh, percentile,
                                percentile_pop, percentile_threshold)
  from .bilateral_rank import bilateral_mean, bilateral_pop
  
  
  __all__ = ['autolevel',
             'bottomhat',
             'equalize',
             'gradient',
             'maximum',
             'mean',
             'meansubstraction',
             'median',
             'minimum',
             'modal',
             'morph_contr_enh',
             'pop',
             'threshold',
             'tophat',
             'noise_filter',
             'entropy',
             'otsu',
             'percentile_autolevel',
             'percentile_gradient',
             'percentile_mean',
             'percentile_mean_substraction',
             'percentile_morph_contr_enh',
             'percentile',
             'percentile_pop',
             'percentile_threshold',
             'bilateral_mean',
             'bilateral_pop']
  
subject: Add __all__ to rank filter package