fixes #70

I would see it more like a cascade of serializers.

wamp.2 => protocol.version
wamp.2.json.batched => protocol.version.lastserializer.firstserializer

```javascript
onmessage = function(data) {
   var msgs = this.unserialize(data);
for(var i=0;i<msgs.length;i++) {
   this._protocol.onmessage(msgs[i]);
}
   
}
,
_unserialize = function(data) {
  var is_list = false;
  for(var i=this.serializers.length-1;i>=0;i--) {
          if(typeof data === "array") {
                is_list = true;
                var _data = [];
                for(var i=0;i<data.length;i++) {
                    _data.append(this.serializers[i].unserialize(data[i]));
                }
                data = _data;
          } else {
             data = this.serializers[i].unserialize(data);
         }
   }
return is_list?data:[data];
}

```

First the "batched" serialiser "unbatches" the data, then the json serialiser unserialises each msg.