Make src/xterm.js ES2015 and export EventEmitter into its own file

Fix #158

src/EventEmitter.js

@@ -0,0 +1,64 @@
+/**
+ * EventEmitter
+ */
+
+function EventEmitter() {
+  this._events = this._events || {};
+}
+
+EventEmitter.prototype.addListener = function(type, listener) {
+  this._events[type] = this._events[type] || [];
+  this._events[type].push(listener);
+};
+
+EventEmitter.prototype.on = EventEmitter.prototype.addListener;
+
+EventEmitter.prototype.removeListener = function(type, listener) {
+  if (!this._events[type]) return;
+
+  var obj = this._events[type]
+  , i = obj.length;
+
+  while (i--) {
+    if (obj[i] === listener || obj[i].listener === listener) {
+      obj.splice(i, 1);
+      return;
+    }
+  }
+};
+
+EventEmitter.prototype.off = EventEmitter.prototype.removeListener;
+
+EventEmitter.prototype.removeAllListeners = function(type) {
+  if (this._events[type]) delete this._events[type];
+};
+
+EventEmitter.prototype.once = function(type, listener) {
+  var self = this;
+  function on() {
+    var args = Array.prototype.slice.call(arguments);
+    this.removeListener(type, on);
+    return listener.apply(this, args);
+  }
+  on.listener = listener;
+  return this.on(type, on);
+};
+
+EventEmitter.prototype.emit = function(type) {
+  if (!this._events[type]) return;
+
+  var args = Array.prototype.slice.call(arguments, 1)
+  , obj = this._events[type]
+  , l = obj.length
+  , i = 0;
+
+  for (; i < l; i++) {
+    obj[i].apply(this, args);
+  }
+};
+
+EventEmitter.prototype.listeners = function(type) {
+  return this._events[type] = this._events[type] || [];
+};
+
+export { EventEmitter };