Implement lpd

As should be defined in BEP-0014. Basically, every 10 seconds a
message to 239.192.152.143:6771 for each torrent, to say that the
peer is in the given swarm.

When a Taipei-Torrent peer receives such a message, it will
automatically connect unless it's already connected.
Re-announce on local every 5 mins
Refactor LPD + clean exit when no LPD
Add support for unregistering ih + refactoring
Various fixes to make it more readable