XHR
http://www.ruanyifeng.com/blog/2012/09/xmlhttprequest_level_2.html
https://developer.mozilla.org/en-US/docs/DOM/XMLHttpRequest
FormData
http://www.cnblogs.com/rubylouvre/archive/2011/04/26/2028827.html
Progress Events
http://www.w3cmm.com/ajax/progress-events.html
