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 summary_frame(self):
      raise NotImplementedError
  
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 7 for calling the Margins obj's underlying member method code with example usage: obj.summary_frame() without return types