Reduce the overhead of multiple serializations when sending messages

[jsjason]

When messages are prepared to be sent, first the key/preValue/value objects are encoded to byte arrays and then serialized again via Avro. This becomes a problem when the message size is big. We should avoid this series of serializations and minimize the serialization overhead. Same as snuspl/dolphin#156.

[wynot12]

I'll close this issue because the old PS module has removed by #1274.