docs: def islitlet_progress(islitlet, islitlet_max):
      """Auxiliary function to print out progress in loop of slitlets.
  
      Parameters
      ----------
      islitlet : int
          Current slitlet number.
      islitlet_max : int
          Maximum slitlet number.
  
      """
      if islitlet % 10 == 0:
          cout = str(islitlet // 10)
      else:
          cout = '.'
      sys.stdout.write(cout)
      if islitlet == islitlet_max:
          sys.stdout.write('\n')
      sys.stdout.flush()