Set an attribute.

        set attributes is actually add a special key, value pair in this dict
        under key = "_meta".

        Usage::

            >>> DT.setattr(d, population=27800000)
            >>> d
            {'_meta': {'population': 27800000, '_rootname': 'US'}}

def setattr(d, **kwarg):
        """Set an attribute.

        set attributes is actually add a special key, value pair in this dict
        under key = "_meta".

        Usage::

            >>> DT.setattr(d, population=27800000)
            >>> d
            {'_meta': {'population': 27800000, '_rootname': 'US'}}
        """
        if _meta not in d:
            d[_meta] = dict()
        for k, v in kwarg.items():
            d[_meta][k] = v