面板收缩(class=collapsed)与扩展(class=expand)
<div ng-init="expand=false" data-ng-class="{'collapsed':expand==false,'expand':expand==true}" data-ng-click="expand=!expand" </div>
http://www.cnblogs.com/lcllao/archive/2012/09/09/2677190.html
http://docs.angularjs.org/guide/directive
http://www.befundoo.com/university/tutorials/angularjs-directives-tutorial/
http://www.ng-newsletter.com/posts/directives.html
http://seanhess.github.io/2013/10/14/angularjs-directive-design.html
http://www.bennadel.com/blog/2447-Exploring-Directive-Controllers-Compiling-Linking-And-Priority-In-AngularJS.htm
http://blog.brunoscopelliti.com/use-cases-of-angularjs-directives
http://amitgharat.wordpress.com/2013/06/08/the-hitchhikers-guide-to-the-directive/
http://www.codeproject.com/Articles/607873/Extending-HTML-with-AngularJS-Directives
http://www.thinkster.io/pick/rep5re7gTM/angularjs-directive-restrictions
http://thecodebarbarian.wordpress.com/2013/09/23/the-8020-guide-to-writing-angularjs-directives/