* Properly encapsulate the mmap/span stuff.
 * Finish balancing socketsPerTorrent and half-open, handshakes and worst conns.
 * Use big.Int, and it's Xor(), and SetBytes() functions for DHT node ID distances.
 * Don't check entire torrent when its added.
 * Add a coarse-responsive download strategy, that prioritizes pieces instead of chunks.
 * Track upload and download data.
 * Remove non-deterministic stuff from unit tests, like the tracker UDP and fuse fs stuff.