Update simpleserialize #7
Description
We presently have a ssz crate which uses the wrong type of serialization. It follows the ethereum/research/py_ssz scheme instead of the ethereum/beacon_chain scheme.
Also, it doesn't decode.
It should follow the beacon_chain serialization format and support encoding and decoding.
We only need it for Blocks and AttestationRecords at the moment, so it would be ideal to prioritize them.