feature(msgpack): Add custom derive macro `Encode` for serialization to `msgpack`

Relates to #96

Custom Encode macro does not yet replace #[derive(Serialize)] as it doesn't support named serialization yet. Also _Encode is a general purpose trait for serialization, so some handling is needed to return only tuples/arrays instead of maps where code expects it (e.g. with Encode<CAN_BE_TUPLE> and ToTupleBuffer: Encode<true>).