CuckooFilter have no Encode/Decode

[lougxing]

hi,

1. I found that other implementations have Encode/Decode interface, why Coook doesn't have it?
   Is it because it is not yet implemented, or because Coook does not support Encode?
2. CuckooFilter use more memory than map[string]struct{} ? keys: 5600000, memory: 7G