TODO

 * Make use of sparse file regions in download data for faster hashing. This is available as whence 3 and 4 on some OS?
 * When we're choked and interested, are we not interested if there's no longer anything that we want?
 * dht: Randomize triedAddrs bloom filter to allow different Addr sets on each Announce.
 * data/blob: Deleting incomplete data triggers io.ErrUnexpectedEOF that isn't recovered from.
 * UL/DL rate-limiting.
 * Handle Torrent being dropped before GotInfo.
 * Track connection chunk contributions to successful and failed piece hashes. Only drop the worst performer on a bad hash. Maybe block its IP.
 * Remove assumptions that the first piece requested will be the first that peers will send.
 * Clean-up DHT transaction code, it's just nasty.
 * Handle wanted pieces more efficiently, it's slow in in fillRequests, since the prioritization system was changed.
 * Determine if we should accept connections, even if we just close them. http://stackoverflow.com/questions/35108571/can-i-leave-sockets-in-syn-recv-until-im-interested-in-accepting
 * Implement BEP 40.
 * Move tracker management code in the torrent package to its own file.