Adds bittorrent support 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.

This patch requires ctorrent to be installed into initramfs.

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_interval 60

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

Seed the initial torrent:
ctorrent live_image.torrent

Boot the live image.