Simplify Session lib wrapper

[bedeho]

Background

The javascript wrapper Session, part of lib, plays a much richer role than the actual libtorrent::session. Among the things it does, is to do internal alert poping, processing, and requesting status updates from torrent and peer plugins. The following excerpt from the constructor is critical to this.

    setInterval(() => {
      // Pop alerts
      var alerts = this.session.popAlerts()

      // Process alerts
      for (var i in alerts) {
        this.process(alerts[i])
      }

      // Request plugin and peer status updates
      for (var [infoHash] of this.torrents.entries()) {
        this.plugin.post_torrent_plugin_status_updates(infoHash)
        this.plugin.post_peer_plugin_status_updates(infoHash)
      }
    }, statusUpdateInterval)

Problem

• An obvious problem with the above is the significant inflexibility it imposes in how this should be done, from the perspective of a library user.
• A second problem is that its part of the obstacle in
  making this wrapper layer thinner, and eventually removing it - or at least making it stateless.

Solution

As a halfway house which solves both issues above, and takes us closer to the final goal, would be to remove the internal timer above entirely, and instead add the following functions that the user calls

• Session.processAlerts()
• Torrent.postTorrentPluginStatusUpdates(infoHash)
• Torrent.postPeerPluginStatusUpdates(infoHash)