Serialize value in MessagePack format

Property definitions

msgpack :: serialization_write $ Writer :: serialize_msgpack
	# Serialize `value` in MessagePack format
	fun serialize_msgpack(value: nullable Serializable, plain: nullable Bool)
	do
		var serializer = new MsgPackSerializer(self)
		serializer.plain_msgpack = plain or else false
		serializer.serialize value
	end
lib/msgpack/serialization_write.nit:165,2--171,4