Update to KDL 2.0

[danini-the-panini]

Pretty much what it says on the box. Since kdl-rb 2.x is fully backwards compatible with v1 (in both syntax and public interface) this should not cause any breaking changes, and can safely be included in a minor version bump.

• Upgrade kdl gem to 2.0.0
• Update config.yml to use new 2.0.0 syntax
• Add warning if config uses v1 syntax

[danini-the-panini]

@karloscarweber This is a trivial update to kdl 2.0

I've noticed now that the Kuddly module uses regexp to parse the line and column from the error message, which got me thinking that it would be beneficial to expose those values directly, which I have done here: danini-the-panini/kdl-rb#20

However that would probably constitute a minor version bump according to semver, so I think I'd like to hold off on pushing that up until we've added some more useful features and interface improvements. If you have any ideas I'd love to hear them!