latex设置itemize形式以及多层itemize
http://tex.stackexchange.com/questions/48036/how-to-represent-cross-and-tick-in-itemize-bullets
文章来自：http://www.cnblogs.com/sumile123/p/5545104.html
http://tex.stackexchange.com/questions/48036/how-to-represent-cross-and-tick-in-itemize-bullets