Use the same handler for binary and text messages

[lpinca]

This merges receiver.onbinary and receiver.ontext into receiver.onmessage.
I think thank using 2 different handlers is pointless.

This is tagged as "major" because it changes the Receiver interface but I don't think many people are using the Receiver and Sender classes directly. Their interface is not documented and imo they should be private and not used directly. Unfortunately they are exposed as static properties of the WebSocket class.

I was also thinking that maybe it makes sense to emit to the WebSocket instance directly instead of using these wrapper functions.

For example we could make the Receiver constructor accept a WebSocket instance, the one the receiver is bound to.

class Receiver {
  constructor (websocket, extensions, maxPayload) {
    this.websocket = websocket;
    ...
  }
}

and then instead of calling the wrapper functions like this, emit the event directly on the websocket object.

this.websocket.emit('message', buf, { binary: true, masked: this.masked });

[lpinca]

I hate that coveralls reports that coverage decreased only because there are fewer lines of code 😑.

[3rd-Eden]

tsk tsk, shame on you @lpinca for writing better code ;-)