varlong 64-bit integer data type (vs varint 32-bit) in protocol data

http://wiki.vg/Protocol#Data_types

According to http://wiki.vg/Protocol#World_Border this 'varlong' type is only used in the world_border packet (0x44 in 1.8, 0x35 in 1.9), for the speed field, minecraft-data specifies using a varint:

            {
              "name": "speed",
              "type": [
                "switch",
                {
                  "compareTo": "action",
                  "fields": {
                    "1": "varint",
                    "3": "varint"
                  },
                  "default": "void"
                }
              ]
            },

Should the type here be a varlong instead? Looks like protodef varint will shift up to 64, but this could be problematic since JavaScript can only natively support up to 53-bit, for 64-bit integers I think we would need something like https://www.npmjs.com/package/node-int64. Other platforms using minecraft-data may also need to handle 32-bit vs 64-bit in their own way (no difference with Python since it'll promote automatically, but C could use int32_t or int64_t, etc.)

Start with the World Border protocol entry and the minecraft-data definition for the speed field shown in the issue. Compare its switch cases with the protocol's VarLong specification and review how ProtoDef's varint decoder handles 64-bit values. Done means the data definition uses the correct type and the behavior is suitable for consumers on platforms with different integer limits.