Given a class, return its docstring.

    If no docstring is present for the class, search base classes in MRO for a
    docstring.

def _schema_get_docstring(starting_class):
    """ Given a class, return its docstring.

    If no docstring is present for the class, search base classes in MRO for a
    docstring.
    """
    for cls in inspect.getmro(starting_class):
        if inspect.getdoc(cls):
            return inspect.getdoc(cls)