拖拽文件实现无刷新上传，支持2G文件

客户端 用HTML5：jQuery File Upload http://blueimp.github.io/jQuery-File-Upload/basic-plus.html 

　　　　　　API https://github.com/blueimp/jQuery-File-Upload/wiki/API

服务器端 用MVC5：ASP .NET Ajax File Upload http://vanacosmin.ro/Articles/Read/AjaxFileUpload

http://commercan.com/2013/07/01/getbufferlessinputstream-vs-getbufferedinputstream/