Add support for libtorrent-2

[DjLegolas]

As there is a new version for libtorrent, Deluge needs to support it in a future release.

This version adds support for BitTorrent v2 specs and more. You can view the upgrade reference at
​https://libtorrent.org/upgrade_to_2.0-ref.html

[OpenDeluge]

I can do the work, but where should I work? Github ?

[DjLegolas]

Yeah, all PR/MR are handled from Github.

And thanks.

[mooninite]

Replying to OpenDeluge:

I can do the work, but where should I work? Github ?

Hi, have you begun working on this?

[Craig]

It appears that at least some of the libtorrent 2 work was done: ​https://github.com/deluge-torrent/deluge/pull/312