run WebTorrent in one process, control it from another process or even another machine. remove clients if we don't hear a heartbeat for this many milliseconds. default 30000 (30 seconds). set to 0 to disable the heartbeat check. once a torrent has no remaining clients, it will be removed. once there are no remaining torrents, the whole webtorrent instance will be destroyed. the webtorrent instance is created lazily the first time a client calls add().