How to add a quit button to this script.

Hi Guys, I have this script (Will Be Bellow) It Works 100% But it doesnt have a quit button. Could someone possibly help me add one bellow the credits bar. here is a screenshot.

But how to add another button with a function to quit the game when i press it?

 //@script ExecuteInEditMode()

var skin:GUISkin; private var gldepth = -0.5; private var startTime = 0.1; var nativeVerticalResolution = 1200.0; var scaledResolutionWidth = nativeVerticalResolution / Screen.height * Screen.width; var mat:Material; private var tris = 0; private var verts = 0; private var savedTimeScale:float; private var pauseFilter; private var showfps:boolean; private var showtris:boolean; private var showvtx:boolean; private var showfpsgraph:boolean; var lowFPSColor = Color.red; var highFPSColor = Color.green; var lowFPS = 30; var highFPS = 50; //var start : GameObject; var url = "WebPlayer.html"; var statColor:Color = Color.yellow; var GuiColor:Color = Color.white;

var crediticons:Texture[];

enum Page { None,Main,Options,Credits }

var currentPage:Page; private var fpsarray:int[]; private var fps:float;

function Start() {

 fpsarray = new int[scaledResolutionWidth];
 Time.timeScale = 1.0;
 PauseGame();

}

function OnPostRender() {

 if (showfpsgraph && mat != null) {

     GL.PushMatrix ();

     GL.LoadPixelMatrix();

     for (var i = 0; i < mat.passCount; ++i)

     {

         mat.SetPass(i);

         GL.Begin( GL.LINES );

         for (var x=0; x<fpsarray.length; ++x) {

             GL.Vertex3(x,fpsarray[x],gldepth);

         }

     GL.End();

     }

     GL.PopMatrix();
     ScrollFPS();
 }

}

function ScrollFPS() {

 for (var x=1; x<fpsarray.length; ++x) {
     fpsarray[x-1]=fpsarray[x];
 }

 if (fps < 1000) {
     fpsarray[fpsarray.length-1] = fps;
 }

}

static function IsDashboard() {

 return Application.platform == RuntimePlatform.OSXDashboardPlayer;

}

static function IsBrowser() {

 return (Application.platform == RuntimePlatform.WindowsWebPlayer || Application.platform == RuntimePlatform.OSXWebPlayer);

}

function LateUpdate () {

 if (showfps || showfpsgraph) {
     FPSUpdate();
 }

 if (Input.GetKeyDown("escape")) {

     switch (currentPage) {

         case Page.None: PauseGame(); break;

         //case Page.Main: UnPauseGame(); break;

         default: currentPage = Page.Main;

     }
 }

}

function OnGUI () {

 if (skin != null) {
     GUI.skin = skin;
 }

 //Our GUI is laid out for a 1920 x 1200 pixel display (16:10 aspect). The next line makes sure it rescales nicely to other resolutions.
 GUI.matrix = Matrix4x4.TRS (Vector3(0, 0, 0), Quaternion.identity, Vector3 (Screen.height / nativeVerticalResolution, Screen.height / nativeVerticalResolution, 1)); 

 ShowStatNums();

 if (IsGamePaused()) {
     GUI.color = GuiColor;

     switch (currentPage) {
         case Page.Main: PauseMenu(); break;

         case Page.Options: ShowToolbar(); break;

         case Page.Credits: ShowCredits(); break;
 
     }
 }   

}

private var toolbarInt:int=0; private var toolbarStrings: String[]= ["Audio","Graphics","Stats","System"];

function ShowToolbar() {

 BeginPage(800,250);
 toolbarInt = GUILayout.Toolbar (toolbarInt, toolbarStrings);

 switch (toolbarInt) {

     case 0: VolumeControl(); break;

     case 3: ShowDevice(); break;

     case 1: Qualities(); QualityControl(); break;

     case 2: StatControl(); break;
 }
 EndPage();

}

function ShowCredits() {

 BeginPage(600,600);

 for (var credit in credits) {
     GUILayout.Label(credit);
 }

 for (var credit in crediticons) {
     GUILayout.Label(credit);
 }

 EndPage();

}

function ShowBackButton() {

 if (GUI.Button(Rect(10,10,150,80),"Back")) {
     currentPage = Page.Main;
 }

}

function ShowDevice() {

 GUILayout.Label ("Unity player version "+Application.unityVersion);

 GUILayout.Label("Graphics: "+SystemInfo.graphicsDeviceName+" "+

 SystemInfo.graphicsMemorySize+"MB    "+

 SystemInfo.graphicsDeviceVersion+"   "+

 SystemInfo.graphicsDeviceVendor);

 GUILayout.Label("Shadows: "+SystemInfo.supportsShadows);

 GUILayout.Label("Image Effects: "+SystemInfo.supportsImageEffects);

 GUILayout.Label("Render Textures: "+SystemInfo.supportsRenderTextures);
 

}

function Qualities() {

 switch (QualitySettings.currentLevel) {

     case QualityLevel.Fastest:

     GUILayout.Label("Fastest");

     break;

     case QualityLevel.Fast:

     GUILayout.Label("Fast");

     break;

     case QualityLevel.Simple:

     GUILayout.Label("Simple");

     break;

     case QualityLevel.Good:

     GUILayout.Label("Good");

     break;

     case QualityLevel.Beautiful:

     GUILayout.Label("Beautiful");

     break;

     case QualityLevel.Fantastic:

     GUILayout.Label("Fantastic");

     break;
 }

}

function QualityControl() {

 GUILayout.BeginHorizontal();

 if (GUILayout.Button("Decrease")) {
     QualitySettings.DecreaseLevel();
 }

 if (GUILayout.Button("Increase")) {
     QualitySettings.IncreaseLevel();
 }
 GUILayout.EndHorizontal();

}

function VolumeControl() {

 GUILayout.Label("Volume");
 AudioListener.volume = GUILayout.HorizontalSlider(AudioListener.volume,0.0,1.0);

}

function StatControl() {

 GUILayout.BeginHorizontal();
 showfps = GUILayout.Toggle(showfps,"FPS");
 showtris = GUILayout.Toggle(showtris,"Triangles");
 showvtx = GUILayout.Toggle(showvtx,"Vertices");
 showfpsgraph = GUILayout.Toggle(showfpsgraph,"FPS Graph");
 GUILayout.EndHorizontal();

}

function FPSUpdate() {

 var delta = Time.smoothDeltaTime;
 if (!IsGamePaused() && delta !=0.0) {
     fps = 1 / delta;
 }

}

function ShowStatNums() {

 GUILayout.BeginArea(Rect(scaledResolutionWidth-200,20,scaledResolutionWidth/4,nativeVerticalResolution/4));

 if (showfps) {
     var fpsString= fps.ToString ("#,##0 fps");
     GUI.color = Color.Lerp(lowFPSColor, highFPSColor,(fps-lowFPS)/(highFPS-lowFPS));
     GUILayout.Label (fpsString);
 }

 if (showtris || showvtx) {
     GetObjectStats();
     GUI.color = statColor;
 }

 if (showtris) {
     GUILayout.Label (tris+"tri");
 }
 if (showvtx) {
     GUILayout.Label (verts+"vtx");
 }
 GUILayout.EndArea();

}

function BeginPage(width,height) { scaledResolutionWidth = nativeVerticalResolution / Screen.height * Screen.width; GUILayout.BeginArea(Rect(scaledResolutionWidth/2 - (width/2), nativeVerticalResolution/2 - (height/2),width,height)); }

function EndPage() {

 GUILayout.EndArea();
 if (currentPage != Page.Main) {
     ShowBackButton();
 }

}

/*function IsBeginning() {

 return Time.time < startTime;

}*/

function PauseMenu() {

 BeginPage(500,300);
 
 if (GUILayout.Button ("Continue")) {
     UnPauseGame();
 }

 if (GUILayout.Button ("Options")) {
     currentPage = Page.Options;
 }

 if (GUILayout.Button ("Credits")) {
     currentPage = Page.Credits;
 }

 if (IsBrowser() && GUILayout.Button ("Restart")) {
     Application.OpenURL(url);
 }

 EndPage();

}

function GetObjectStats() {

 verts = 0;
 tris = 0;
 var ob = FindObjectsOfType(GameObject);
 for (var obj in ob) {
     GetObjectStats(obj);

 }

}

function GetObjectStats(object) {

 var filters : Component[];
 filters = object.GetComponentsInChildren(MeshFilter);
 for( var f : MeshFilter in filters ){
     tris += f.sharedMesh.triangles.Length/3;
     verts += f.sharedMesh.vertexCount;
 }

}

function PauseGame() {

 savedTimeScale = Time.timeScale;

 Time.timeScale = 0;

 AudioListener.pause = true;

 if (pauseFilter) pauseFilter.enabled = true;

 currentPage = Page.Main;
 
 transform.position = new Vector3(0, 1, 0);
 Screen.lockCursor = false;

}

function UnPauseGame() {

 Time.timeScale = savedTimeScale;

 AudioListener.pause = false;

 if (pauseFilter) pauseFilter.enabled = false;

 currentPage = Page.None;

 transform.position = Vector3.zero;
 Screen.lockCursor = true;

}

function IsGamePaused() { return Time.timeScale == 0; }

function OnApplicationPause(pause:boolean) {

 if (IsGamePaused()) {
     AudioListener.pause = true;
 }

}