A convenience function for passing negative values to increment.

        Keyword arguments:
        key -- the key the item is stored under. Required.
        cache -- the cache the item belongs to. Defaults to None, which uses
                 self.name. If no name is set, raises a ValueError.
        amount -- the amount to decrement the value by. Can be negative to
                  increment the value. Defaults to 1.

def decrement(self, key, cache=None, amount=1):
        """A convenience function for passing negative values to increment.

        Keyword arguments:
        key -- the key the item is stored under. Required.
        cache -- the cache the item belongs to. Defaults to None, which uses
                 self.name. If no name is set, raises a ValueError.
        amount -- the amount to decrement the value by. Can be negative to
                  increment the value. Defaults to 1.
        """
        amount = amount * -1

        return self.increment(key=key, cache=cache, amount=amount)