*`Node::Identity()` is removed, and `Node::IsAlias()` and `Node::IsReferenced()` have been merged into `Node::IsAliased()`. The reason: there's no reason to distinguish an alias node from its anchor - whichever happens to be emitted first will be the anchor, and the rest will be aliases.
*`Node::Read<T>` is now `Node::to<T>`. This wasn't a documented function, so it shouldn't break anything.
*`Node`'s comparison operators (for example, `operator == (const Node&, const T&)`) have all been removed. These weren't documented either (they were just used for the tests), so this shouldn't break anything either.
* The emitter no longer produces the document start by default - if you want it, you can supply it with the manipulator `YAML::BeginDoc`.