send() method to return true explicitly when success and return an error...

Third party developers are not able to know if kakao.link(app_name).send() has successfully executed or it failed to launch the app as the library doesn't provide any explicit return value or raise exceptions. This PR changes send() method's behaviour that the method always returns a value so the 3rd-party developers can handle it accordingly.

Usage:
```html
<script type="text/javascript" src="./kakao.link.js"></script>
<script>
var response = function executeKakaoStoryLink() {
    kakao.link("story").send({   
        post : "http://m.media.daum.net/entertain/enews/view?newsid=20120927110708426",
        appid : "m.media.daum.net",
        appver : "1.0",
        appname : "미디어다음",
        urlinfo : JSON.stringify({title:"(광해) 실제 역사적 진실은?", desc:"(광해 왕이 된 남자)의 역사성 부족을 논하다.", imageurl:["http://m1.daumcdn.net/photo-media/201209/27/ohmynews/R_430x0_20120927141307222.jpg"], type:"article"})
    });
    if ( response !== true ) {
        alert(response); // the developer can handle the error.
    }
  }
</script>
```