Replace response engines with serializers, same job but organized better, read README.md , no front-end changes if you used default engines.

HISTORY.md

@@ -2,6 +2,19 @@
 
 **How to upgrade**: remove your `$GOPATH/src/github.com/kataras/iris` folder, open your command-line and execute this command: `go get -u github.com/kataras/iris`.
 
+## 4.2.0 -> 4.2.1
+
+- **CHANGE**: No front-end changes if you used the default response engines before. Response Engines to Serializers, `iris.ResponseEngine` `serializer.Serializer`, comes from `kataras/go-serializer` which is installed automatically when you upgrade iris with `-u` flag.
+
+    - the repo "github.com/iris-contrib/response" is a clone of "github.com/kataras/go-serializer", to keep compatibility state. examples and gitbook updated to work with the last.
+
+    - `iris.UseResponse(iris.ResponseEngine, ...string)func (string)` was used to register custom response engines, now you use: `iris.UseSerializer(key string, s serializer.Serializer)`.
+
+    - `iris.ResponseString` same defintion but differnet name now: `iris.SerializeToString`
+
+[Serializer examples](https://github.com/iris-contrib/examples/tree/master/serialize_engines) and [Book section](https://kataras.gitbooks.io/iris/content/serialize-engines.html) updated.
+
+
 ## 4.1.7 -> 4.2.0
 
 - **ADDED**: `iris.TemplateSourceString(src string, binding interface{}) string` this will parse the src raw contents to the template engine and return the string result & `context.RenderTemplateSource(status int, src string, binding interface{}, options ...map[string]interface{}) error` this will parse the src raw contents to the template engine and render the result to the client, as requseted [here](https://github.com/kataras/iris/issues/409).