https://docs.angularjs.org/guide/directive
https://docs.angularjs.org/api/ng/service/$compile
https://docs.angularjs.org/guide/compiler
https://docs.angularjs.org/api/ng/service/$interpolate
https://docs.angularjs.org/api/ng/provider/$compileProvider#directive
http://www.ifeenan.com/angularjs/2014-09-04-%5B%E8%AF%91%5DNG%E6%8C%87%E4%BB%A4%E4%B8%AD%E7%9A%84compile%E4%B8%8Elink%E5%87%BD%E6%95%B0%E8%A7%A3%E6%9E%90/