This PR includes a new package called testrouting, which implements a very algorithmically slow but hopefully easy-to-keep-operationally-correct in-memory routing table. The routing table also supports writing out its current structure as a DOT graph for visualization. testrouting is primarily meant to help in coming up with generic routing table integration tests.
This PR also includes a new routing table integration test suite that runs against all current routing table implementations. Our existing routing table passes a lot of the tests, but not all of them, still debugging why. I have confirmed the tests should pass with the visualization graphs though.
We realized that the Kademlia FindNear() function was
1. not using XOR distance (AKA _totally broken_)
2. largely a duplicate of the RoutingTable FindNear() function
Changes in this PR:
1. upgraded RoutingTable FindNear() to use iterator and restrictions
2. removed unneeded RoutingTable interface
3. made Kademlia wrap methods that were previously accessed via RoutingTable
4. fixed the tests
