* Properly encapsulate the mmap/span stuff.
 * Track upload and download data.
 * Emulate a UDP server in the UDP tracker tests.
 * Make use of sparse file regions in download data for faster hashing.
 * Add an alternative to mmap()'ed torrent data.
 * If we're choked and interested, we never send not-interested if there's nothing we want?
 * Perform announce as part of GetPeers, to reduce closest node calculation overhead, and wasting discarded nodes during the search.