基于白名单清理 html 标签的 pkg: gosanitize

[gihnius]

https://github.com/gihnius/gosanitize

基于这个代码: https://github.com/mjibson/goread/tree/master/sanitizer

为了应付这个： http://www.qufor.com/topics/53609e957cc1f85101000002

欢迎 fork, 添加测试！