query forwarding

If a peer X sends a query but peer Y has no results for the query, X can ask Y to ask Y's peers (who are not also connected to X) about the query. However, for this to work in practice we'd also need a mechanism for relaying the hypercore data without necessarily saving it to disk and perhaps not even knowing about the content at all. Relaying data ought to have much lower latency than establishing a new connection, at the expense of lower throughput and more network traffic.