update callback url doc
fix fetchwhensave doc error
Merge branch 'master' of github.com:leancloud/avoscloud-doc

Conflicts:
	sns.md
Merge pull request #35 from lbt05/master

修正fetchWhenSave的文档错误
Fixed link.
更新云代码Web Hosting和备案
Merge branch 'master' of github.com:avoscloud/avoscloud-doc
添加云代码备案的身份证要求
Merge remote-tracking branch 'upstream/master' into feature/bigquery