birdnotes.py: Objects to represent bird note files

This method generates the elements of self._dayList without changing their order. (If they were put in out of chronological order, that's how they will come out.)

# - - -   B i r d N o t e S e t . g e n D a y s

    def genDays(self):
        """Generate the DayNotes elements of self.
        """
        for  day in self._dayList:
            yield day