回帖：https://developer.qiniu.com/kodo/manual/1206/put-policy
https://developer.qiniu.com/kodo/manual/1208/upload-token
http://jssdk.demo.qiniu.io/formdata
https://developer.qiniu.com/kodo/manual/1272/form-upload
https://developer.qiniu.com/kodo/sdk/1283/javascript