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

Fix #158

addons/attach/attach.js

@@ -21,7 +21,7 @@
     /*
      * Plain browser environment
      */
-    attach(this.Xterm);
+    attach(window.Terminal);
   }
 })(function (Xterm) {
   'use strict';

addons/fit/fit.js

@@ -26,7 +26,7 @@
     /*
      * Plain browser environment
      */
-    fit(this.Xterm);
+    fit(window.Terminal);
   }
 })(function (Xterm) {
   /**

addons/fullscreen/fullscreen.js

@@ -25,7 +25,7 @@
     /*
      * Plain browser environment
      */
-    fullscreen(this.Xterm);
+    fullscreen(window.Terminal);
   }
 })(function (Xterm) {
   var exports = {};

addons/linkify/linkify.js

@@ -13,7 +13,7 @@
     /*
      * Plain browser environment
      */
-    linkify(this.Xterm);
+    linkify(window.Terminal);
   }
 })(function (Xterm) {
   'use strict';