Return stats for the given year and month.

def get_stats(self, year=None, month=None):
        """Return stats for the given year and month."""
        parts = ['my', 'stats']
        if month and not year:
            raise ValueError("month cannot be specified without year")
        if year:
            parts.append(year)
        if month:
            parts.append(year)
        url = self._build_url(*parts)
        return self._json(url)