Feature Request: TTL only Cache

[elbaro]

1. Unlimited sized Cache

@Memoize(Cache("unlimited"), timedelta(seconds=10 * 60))
def get():
    ...

2. Zero sized Cache (ignore returned value)

@Memoize(Cache("empty"), timedelta(seconds=10 * 60))
def update_global_dict():
    value = query(..)
    global_dict[value.field2] = value.field1
    global_dict[value.field3] = value.field1