Change CommonJS package structure

Instead of making Xterm prototype extending optional, just require Xterm and pass it as parameter to the function just like it is being done with RequireJS

addons/fullscreen/fullscreen.js

@@ -15,7 +15,7 @@
     /*
      * CommonJS environment
      */
-    module.exports = fullscreen.call(this);
+    module.exports = fullscreen(require('../../src/xterm'));
   } else if (typeof define == 'function') {
     /*
      * Require.js is available
@@ -44,24 +44,9 @@
     term.element.classList[fn]('fullscreen');
   };
 
-  /**
-   * Extends the given terminal prototype with the public methods of this add-on.
-   *
-   * @param {function} Xterm - The prototype to be extended.
-   */
-  exports.extendXtermPrototype = function (Xterm) {
-    Xterm.prototype.toggleFullscreen = function (fullscreen) {
-      exports.toggleFullScreen(this, fullscreen);
-    };
+  Xterm.prototype.toggleFullscreen = function (fullscreen) {
+    exports.toggleFullScreen(this, fullscreen);
   };
 
-  /**
-   * If the Xterm parameter is a function, then extend it with the methods declared in this
-   * add-on.
-   */
-  if (typeof Xterm == 'function') {
-    exports.extendXtermPrototype(Xterm);
-  }
-
   return exports;
 });