Modifiable answer checker in reviews and lessons
此脚本不应直接安装。它是供其他脚本使用的外部库，要使用该库请加入元指令 // @require https://update.greasyfork.icu/scripts/470201/1215595/WaniKani%20Answer%20Checker.js
TypeScript definition at https://github.com/patarapolw/wanikani-userscript/tree/master/userscripts/types/answer-checker.d.ts