sieveLau

change cipher to aes-128-gcm

2

What this does: 1. split the javascript used for decryption into a seperate file 2. change cipher from aes-cbc to aes-gcm About 1, pros and cons are described in #20...

the src link of decrypt.js in `hugo_encryptor.py` should be replaced with [https://cdn.jsdelivr.net/gh/Li4n0/hugo_encryptor@master/decrypt.js](https://cdn.jsdelivr.net/gh/Li4n0/hugo_encryptor@master/decrypt.js), so users don't need to copy it into the `static` folder. 在已合并的pull request #21 中提到的decrypt.js的链接，由于当时没有merge所以无法生成jsdelivr的cdn链接。merge之后可以生成了，所以为了让用户不用自己复制js到static目录，建议修改script block的src链接。