This is a change to how packets are transferred; the API has not been changed.
While the difference may be unnoticable when using unencrypted packets, because of MessagePack's compact size and better handling of byte values encrypted packets should transfer faster.
This commit removes the org.JSON library where alternatives are already provided (Bungee & Bukkit provide Gson). This change was made to improve compatability with BungeeCord plugins and reduce file sizes.
This means big changes to the SubData API, which heavily relied on org.JSON. Now we submit our data through YAMLSection to be converted and sent over the network.