Update to 4.0.0-alpha.3 - Response Engines, 'inject' the context.JSON/JSONP/Text/Data/Markdown/Render, Read HISTORY.md

## 4.0.0-alpha.2 -> 4.0.0-alpha.3

**New**

A **Response Engine** gives you the freedom to create/change the
render/response writer for

- `context.JSON`
- `context.JSONP`
- `context.XML`
- `context.Text`
- `context.Markdown`
- `context.Data`
- `context.Render("my_custom_type",mystructOrData{},
iris.RenderOptions{"gzip":false,"charset":"UTF-8"})`
- `context.MarkdownString`
- `iris.ResponseString(...)`

**Fix**
- https://github.com/kataras/iris/issues/294

**Small changes**

- `iris.Config.Charset`, before alpha.3 was `iris.Config.Rest.Charset` &
`iris.Config.Render.Template.Charset`, but you can override it at
runtime by passinth a map `iris.RenderOptions` on the `context.Render`
call .
- `iris.Config.IsDevelopment` , before alpha.1 was
`iris.Config.Render.Template.IsDevelopment`

**Websockets changes**

No need to import the `github.com/kataras/iris/websocket` to use the
`Connection` iteral, the websocket moved inside `kataras/iris` , now all
exported variables' names have the prefix of `Websocket`, so the old
`websocket.Connection` is now `iris.WebsocketConnection`.

Generally, no other changes on the 'frontend API', for response engines
examples and how you can register your own to add more features on
existing response engines or replace them, look
[here](https://github.com/iris-contrib/response).

**BAD SIDE**: E-Book is still pointing on the v3 release, but will be
updated soon.

websocket/emitter.go

@@ -1,50 +0,0 @@
-package websocket
-
-const (
-	// All is the string which the Emitter use to send a message to all
-	All = ""
-	// NotMe is the string which the Emitter use to send a message to all except this connection
-	NotMe = ";iris;to;all;except;me;"
-	// Broadcast is the string which the Emitter use to send a message to all except this connection, same as 'NotMe'
-	Broadcast = NotMe
-)
-
-type (
-	// Emitter is the message/or/event manager
-	Emitter interface {
-		// EmitMessage sends a native websocket message
-		EmitMessage([]byte) error
-		// Emit sends a message on a particular event
-		Emit(string, interface{}) error
-	}
-
-	emitter struct {
-		conn *connection
-		to   string
-	}
-)
-
-var _ Emitter = &emitter{}
-
-// emitter implementation
-
-func newEmitter(c *connection, to string) *emitter {
-	return &emitter{conn: c, to: to}
-}
-
-func (e *emitter) EmitMessage(nativeMessage []byte) error {
-	mp := messagePayload{e.conn.id, e.to, nativeMessage}
-	e.conn.server.messages <- mp
-	return nil
-}
-
-func (e *emitter) Emit(event string, data interface{}) error {
-	message, err := serialize(event, data)
-	if err != nil {
-		return err
-	}
-	e.EmitMessage([]byte(message))
-	return nil
-}
-
-//