STREAMING_TODO

Streaming steps:

OK	home-made JSON.stringify() that supports circular references
	since it will be slower than native JSON.stringify(), use it only on populated documents.
	It is not needed anymore for RestQuery to clone document when populating other documents.

	JSON stringify() is streamed: it creates a Stream object, it uses generators, it does not retain anything

	RootsDB/RestQuery streams: does not retain documents, use MongoDB cursors to create a RootsDB stream, RestQuery will
	stream thing back to the client (access right will be streamed too), the client will receive "flat" data in the
	JSON stream format (one JSON per line) with a trailing JSON containing information about how to re-structure data.