Socket.io like WebSockets

**Subsystem**
WebSocket

**Is your feature request related to a problem? Please describe.**
It's not related to any problem.

**Describe the solution you'd like**
It would be nice to have [socket.io](https://socket.io/) like interface for [WebSockets].
For e.g. Interface like that would be nice:

```kotlin
webSocket("/") { socket->
// Emit value from server on "chat-message".
socket.emit("chat-message", Frame.Text("YOU SAID $text"))

// Below block will be executed whenever value will be emitted in "response".
socket.on("response") { response->
// Response received from client on "response".
}
}
```

**Motivation to include to ktor**
If such feature is implemented in ktor it'll make development much more easier. It'll help to make communication better among server and client. It'll provide high reliability.