code: def addlist(self, key, valuelist=[]):
          
          for value in valuelist:
              self.add(key, value)
          return self
docs: Add the values in <valuelist> to the list of values for <key>. If <key>
          is not in the dictionary, the values in <valuelist> become the values
          for <key>.
  
          Example:
            omd = omdict([(1,1)])
            omd.addlist(1, [11, 111])
            omd.allitems() == [(1, 1), (1, 11), (1, 111)]
            omd.addlist(2, [2])
            omd.allitems() == [(1, 1), (1, 11), (1, 111), (2, 2)]
  
          Returns: <self>.