Adds bittorrent support to 45url-lib for live images

This patch adds bittorrent support to 45url-lib for those that might want
to retrieve the same live image for multiple systems at once without
saturating the network.

Torrent kernel command line format:
root=live:torrent://example.com/liveboot.img.torrent

Start a tracker:
bttrack --bind <tracker_ip> --port 6969 --dfile dstate --reannounce_interv

Create the torrent:
ctorrent -t live_image -u http://<tracker_ip>:6969/announce -s live_image.

Seed the initial torrent:
ctorrent live_image.torrent

Boot the live image.