GitLab

Updated the node/value classes with the new iterators, they compile until we try to instantiate anything

Made the 'data' member optional in node_ref - it's only created on-demand, so we don't waste extra memory every time we do Value tmp = v;

Switched memory to using shared nodes, and node_data to keep only naked node pointers, not shared nodes (to break the cycle, and we don't need weak pointers because their memory is guaranteed to exist, via 'memory')