Prepare release 4.0.0

README.md

@@ -32,6 +32,65 @@ Please read [CONTRIBUTING.md](CONTRIBUTING.md) for guidelines.
 
 # Changelog
 
+## Version 4.0.0
+
+This a major release that introduces a few breaking changes.
+
+### Breaking changes
+
+* **The constructors of `Serializer` and `Deserializer` are now obsolete**  
+  Except for the parameterless versions. The `SerializerBuilder` and `DeserializerBuilder`
+  classes should now be used to configure and create instances of the (de)serializer.
+
+* **Replaced the `IYamlSerializable` interface with `IYamlConvertible`**  
+  The `IYamlSerializable` is now obsolete, but will be kept until the next major release.
+
+* **[Removed](https://github.com/aaubry/YamlDotNet/pull/203) `EventReader`**  
+  `EventReader` was a wrapper over `IParser` that offered some abstractions for parsing,
+  but also had some design flaws. It has been replaced by extension methods for `IParser`.
+  The extension methods provide the same functionality,
+  and allow to always use the same type to represent the parser.
+
+* **Dropped support for `YamlAliasAttribute`**  
+  This class has been obsolete for many releases, and it was time to let it go.
+
+### New features
+
+* [**`SerializerBuilder` and `DeserializerBuilder`**](https://github.com/aaubry/YamlDotNet/pull/204)  
+  This is an important change that adds "builders" that can be used
+  to configure the Serializer and Deserializer through a fluent syntax.
+  The main objective of this is to allow more control over
+  the composition of services performed by these two classes.
+  This means that every aspect of the composition should be
+  extensible / overridable. Things like injecting a custom TypeInspector
+  or replacing the the default ArrayNodeDeserializer with
+  an alternative implementation become possible and easy.  
+  In order to avoid breaking existing code,
+  the constructors of Serializer and Deserializer have been kept
+  but marked as obsolete. In a future release they will be discarded.
+
+* **Added the `IYamlConvertible` interface**  
+  This new interface differs in that its methods receive a delegate that can be used
+  to reuse the current serializer or deserializer.
+
+* **Improved the usability of `YamlDocument`**  
+  and other RepresentationModel classes:
+  * Added conversion operators and indexers for easier parsing and construction of YamlNodes.
+  * `YamlMappingNode`, `YamlSequenceNode` and `YamlScalarNode` now implement `IYamlConvertible`,
+    which means that these types can appear in the middle of an object that is being serialized or
+    deserialized, and produce the expected result.
+
+* [**Added support for alternative Boolean values**](https://github.com/aaubry/YamlDotNet/pull/183)
+  * True: `true`, `y`, `yes`, `on`
+  * False: `false`, `n`, `no`, `off`.
+
+
+### Bug fixes
+
+* [Serialization Error when string starts with quote](https://github.com/aaubry/YamlDotNet/issues/135)
+* [YamlVisitor is marked as obsolete, but no YamlVisitorBase class exists](https://github.com/aaubry/YamlDotNet/issues/200)
+* Do not assign anchors to scalars during serialization.
+
 ## Version 3.9.0
 
 New features: