add setting enable_trackers

[milahu]

allow to disable trackers in settings

similar settings

• active_tracker_limit
• enable_dht
• enable_lsd
• enable_upnp
• enable_natpmp

workaround: remove trackers from the torrent file before passing it to libtorrent.torrent_info

import io
import torf
import libtorrent as lt
settings = lt.default_settings()
# settings['enable_trackers'] = False # TODO implement in libtorrent
settings['active_tracker_limit'] = 0 # disable trackers # FIXME not working
ses = lt.session(settings)
# ti = lt.torrent_info("test.torrent")
# ti.trackers = lambda: [] # not working
# there is ti.add_tracker but no ti.remove_tracker or ti.remove_trackers
# use torf to remove trackers
# NOTE torf does not support v2 torrents
torrent = torf.Torrent.read("test.torrent")
torrent.trackers = [] # remove trackers
buf = io.BytesIO()
torrent.write_stream(buf)
ti = lt.torrent_info(buf.getvalue())
del buf
# ti.trackers = lambda: [] # not working
# there is ti.add_tracker but no ti.remove_tracker or ti.remove_trackers
atp = lt.add_torrent_params()
atp.ti = ti
atp.save_path = "."
atp.trackers = []  # disable trackers # FIXME not working
th = ses.add_torrent(atp)

disabling trackers is possible in anacrolix-torrent

type ClientTrackerConfig struct {
	// Don't announce to trackers. This only leaves DHT to discover peers.
	DisableTrackers bool `long:"disable-trackers"`