http://www.cocoachina.com/bbs/read.php?tid-89985-page-1.html
http://www.jianshu.com/p/44629e5bf986
http://www.jianshu.com/p/a0e3c77d3164
http://blog.csdn.net/u013252770/article/details/51463482
ios表单上传图片或文件
原文：http://www.cnblogs.com/yeng/p/6372151.html
