Add seeds/leechers stats

[comtom]

For old torrents is hard to know if they are still active, adding seed and leech count to the metadata can help a user decide which is the best torrent to get.

If this idea is hard to implement, maybe is helpful to add a "last seen" timestamp, indicating when was seen active for the last time.
Also this can be extended to remove "old" torrents that didn't had activity for an arbitrary amount of time.

this project is great, thank you for keeping it alive.