Serialize blockchain data / tx data to binary

Currently we are communicating through `JSON`.
While this is great for readability, it uses a lot more bandwidth / memory than it should and will make it hard to scale. It also starts to show problems such as [this](https://github.com/bosnet/sebak/issues/412).

We should switch to something a lightweight format. Bitcoin and ethereum use a simple binary serialization, Stellar uses XDR, and I'm pretty certain some chains do use protobuf.
I am personally leaning towards binary because it's the simplest, more lightweight format.