Generator that converts a doc to a sequence of lines.
        :param doc: A dictionary
        :param format_func: customisable formatter defaults to pformat
        :return: a generator yielding a line at a time

def doc_to_lines(self, doc, format_func=None):
        """
        Generator that converts a doc to a sequence of lines.
        :param doc: A dictionary
        :param format_func: customisable formatter defaults to pformat
        :return: a generator yielding a line at a time
        """
        if format_func:
            for l in format_func(doc).splitlines():
                yield l
        elif self.pretty_print:
            for l in pprint.pformat(doc).splitlines():
                yield l
        else:
            for l in str(doc).splitlines():
                yield l