updated messi.js to correct when messi appears off page

added a slightly modified version of the nudge function  from Nicolas Honing's popup.js (https://github.com/nhoening/popup.js/) that will prevent messi from appearing off the page when using manual positioning

ex:
----------------------------------------------------------------------------------------------------------------------------------
<p style="position:absolute; top:200px; left: 800px;"> TEST hover performance using modified messi</p>
<span class="test" style="position:absolute; top:20px; left: 10px;">test</span>
<span class="test" style="position:absolute; top:20px; left: 1500px;">test</span>
<span class="test" style="position:absolute; top:1000px; left: 10px;">test</span>
<span class="test" style="position:absolute; top:1000px; left: 1500px;">test</span>
<span class="test" style="position:absolute; top:400px; left: 1000px;">test</span>

<script type="text/javascript">

 $( document ).ready(function(){
 
	console.log("loaded");
	var popup;
	$('.test').on('mouseover', function(e){
		
		popup = new Messi('This is a message with Messi.', {closeButton : false, center: false, viewport : { top: ( e.pageY.toString()+"px"), left: ( e.pageX.toString()+"px")} });
		
	});
	$('.test').on('mouseout', function(e){ if (typeof popup === "object" ){ popup.hide(); } });
	
 });