1:  PURPOSE
	use the event loop idea, to monitor the data change, currently in front-end world, we get the data from 
	the back-end ,and show the data , if data change , we need do some action, so the purpose is : design a data
	driven framework. the watcher.js is the test for that .

2:  HOW TO USE IT?
	in the Observer.js, we have the viewModel (which come from the MVVM), so :
	
	//user view Model
	var myviewModel={
	targetAttr:¡®some value¡¯
	};
	
	//start watch
	watcher.startWatch();
	
	watcher.watchUtil(¡®targetAttr¡¯,myviewModel,function(){
	   // this is the user define function, this function will check whether the targetAttr value change
	   return true/false;
	}).do(function(){
	  //if data change, do some action
	});

3:  Bugs.
    watcher.stopWatch() do not work
	
4:  TODO:
    a: will implement removeWatchTarget method
	b: add test report under IE6/7
	c: consider the complex senario
	d: consider the dependance between watcher, avoid the endless loop