Associate object to id

Property definitions

serialization $ DeserializerCache :: []=
	# Associate `object` to `id`
	fun []=(id: Int, object: Object) do received[id] = object
lib/serialization/caching.nit:99,2--100,58

serialization $ DuplexCache :: []=
	redef fun []=(id, object)
	do
		super
		assert object isa Serializable
		sent[object] = id
	end
lib/serialization/caching.nit:115,2--120,4