-track contact failures, last replied, and last requested. use this to provide a 'contact_is_good' property on Contact objects
-ensure no duplicate contact objects are created
-remove confusing conflation of node id strings with Contact objects, update docstrings
-move RPC failure tracking to a callback/errback pair in sendRPC (so the contact is only updated once)
-handle seed nodes during the join sequence by setting their node ids after they initially reply to our ping
-name all of the kademlia RPC keyword args, remove confusing **kwargs and dictionary parsing
-add host ip/port to DHT send/receive logging to make the results comprehensible when running many nodes at once
-adds reactor (clock) and reactor functions listenUDP, callLater, and resolve as arguments to Node.__init__
-set the reactor clock on LoopingCalls to make them easily testable
-convert callLater manage loops to LoopingCalls
When a k-bucket does not contain enough close nodes, the
DHT will look into neighbouring k-buckets in order to entend
the list of returned nodes.
However, the list should not be extended beyond its maximum size.
Signed-off-by: Antonio Quartulli <antonio@mandelbit.com>