feature/network_nbt

[MSKatKing]

I've implemented NetEncode and NetDecode for NBT types. Here's how it works:

We have a struct, NBT, which is just a wrapper around T.

This type, when T: NBTSerializable, implement NetEncode. The NBTSerializable trait has been modified to use a std::io::Write instead of a hard-coded Vec. It's also been given an async version of the serialize fn. The NetEncode implementation basically just calls these functions for T.

NBT also implements NetDecode when T: for<'a> FromNbt<'a>. NetDecode works a little differently. It will first read the data into a Vec, then create a new NbtTape, finally using that to deserialize into T.

NBT implements Deref<Output=T> and DerefMut, so you can access fields of T without unwrapping it. To use it, just place NBT on the packet field you want to have serialized/deserialized to/from NBT.

This is still a draft PR because I have not tested it yet. Once I know it works, I'll submit this for review.

[MSKatKing]

Can confirm it works, I tested it with the play Disconnect packet and the packet sent as normal and the client recognized it and displayed the correct message.

[Sweattypalms]

lgtm