'Adds items to one or more lists.
**Usage Example**::
feed_counters = ListsStorage(\'user:5\')
feed_counters.add(unread=[1,2,3,4], unseen=[1,2,3])
feed_counters.add(unread=[5,6])
feed_counters.add(unseen=[7,8])
: kwargs define pairs of list and items to be used for lists modifications'

def add(self, **kwargs):

    raise NotImplementedError()
