Add pkg: server/list/players.
server: Refactoring + Add missing docs.

- math/rand import renambed: prand -> mrand.
- BroadcastOthers, BroadcastMessage, AddPlayer and RemPlayer methods are
now embedded from players.List.
- Handle method is now hidden (handle).
- Token method removed. Only required in 0x02, move it there.
types/minecraft: Fix Metadata R/W + Add tests.
proto/packet: mct.Metadata isn't a pointer now.