Arreglar referencia al mismo EventTarget (#172)

* Arreglar referencia al mismo EventTarget

* lint?

* hopefully this lints, bc I cant run the linter

* last lint attempt

* Lint

js/karel.js

@@ -85,10 +85,9 @@ var Runtime = function (world) {
   self.disableStackEvents = false;
 
   self.load([['HALT']]);
+  self.events = new EventTarget();
 };
 
-Runtime.prototype = new EventTarget();
-
 Runtime.HALT = 0;
 Runtime.LINE = 1;
 Runtime.LEFT = 2;
@@ -118,6 +117,22 @@ Runtime.CALL = 25;
 Runtime.RET = 26;
 Runtime.PARAM = 27;
 
+Runtime.prototype.addEventListener = function (type, listener) {
+  this.events.addEventListener(type, listener);
+};
+
+Runtime.prototype.removeEventListener = function (type, listener) {
+  this.events.removeEventListener(type, listener);
+};
+
+Runtime.prototype.dispatchEvent = function (evt) {
+  this.events.dispatchEvent(evt);
+};
+
+Runtime.prototype.fireEvent = function (type, properties) {
+  this.events.fireEvent(type, properties);
+};
+
 Runtime.prototype.load = function (opcodes) {
   var self = this;
   var opcode_mapping = [