class_docstr: Mostly a do nothing class. Lays out the methods expected of a sub-class.
  
  This is just a sketch of what we may want out of a general margins class.
  I (SS) need to look at details of other models.
code: def get_margeff(self, *args, **kwargs):
      self._reset()
      self.margeff = self.get_margeff(*args)
  
imports: from statsmodels.compat.python import lzip
  import numpy
  from scipy.stats import norm
  from statsmodels.tools.decorators import cache_readonly
label_desc: Use image node_id 3 for calling the Margins obj's underlying member method code with example usage: obj.get_margeff() without return types