Macro packet 

macro_rules! packet {
    (
        $(#[$meta:meta])*
        $vis:vis struct $Name:ident {
            $( $fvis:vis $field:ident : $ty:ty ),* $(,)?
        }
    ) => { ... };
}

Declare a typed packet struct whose fields are automatically encoded/decoded.

All field types must implement PacketField: bool, i32, i64, u32, u64, f32, f64, String, Vec<u8>.

use yog_network::{packet, Packet};

packet! {
    pub struct PingPacket {
        seq: u32,
        message: String,
    }
}

let p = PingPacket { seq: 1, message: "hello".into() };
let decoded = PingPacket::decode(&p.encode()).unwrap();
assert_eq!(decoded.seq, 1);