浏览器缓存相关http header mark
1.expires
2.if-modified-since&last-modified
3.if-none-match&etag
4.cache-control:no-cache OR max-age
5.pragma:no-cache
https://zhuanlan.zhihu.com/p/33356918
http://www.cnblogs.com/slly/p/6732749.html#3673406
http://acooly.iteye.com/blog/1317272