KDL 2.0 compliance

[zkat]

KDL 2.0.0-draft.3 is now generally available (kdl-org/kdl#286), and with it, we've decided to encourage existing implementations to start working towards 2.0 support and send feedback and suggestions for anything you might run into, so I'm making this tracking issue. :)

[Exidex]

@zkat What is the story with backwards compatibility. Is the plugin expected to support both? or do we throw away v1 support?

[zkat]

I intend to throw away v1 support going forward, with the expectation that 2.0 will be the only version actually in use, and 1.0 will just be historical