Rewriting the chrome extension with manifest v3

Currently:
* The background page and popup page seem to be working fine
* Cleaned up a lot of code and rewrote them to use more morden JS features like async/await/modules
* Restructured the folder structure to make more sense; and reformatted some files to use a better coding style

Still need to:
* Fix the options page for setting custom proxy server
* Make the header modifieer work with manifest v3
* Change the remaining files to comply with the code style

.eslintrc.js

@@ -0,0 +1,20 @@
+module.exports = {
+  env: {
+    es2021: true,
+    browser: true,
+    webextensions: true,
+    node: true,
+    jquery: true,
+  },
+  extends: [
+    'google',
+  ],
+  parserOptions: {
+    ecmaVersion: 'latest',
+    sourceType: 'module',
+  },
+  rules: {
+    'require-jsdoc': 'off',
+    'max-len': ['error', {'code': 100}],
+  },
+};

README.md

@@ -1,10 +1,6 @@
 # Unblock Youku
 
-This project contains two parts (closely related with shared JavaScript code).
-
-1. A _Google Chrome extension_ helping users access their web services while travelling outside mainland China. You can find this extension on Chrome Web Store at [http://uku.im/chrome](http://uku.im/chrome).
-
-2. A Node.js based _backend server_ that supports the redirect mode of the Chrome extension. [![Build Status](https://travis-ci.org/uku/Unblock-Youku.svg?branch=master)](https://travis-ci.org/uku/Unblock-Youku)
+ A Chrome extension helping users access their web services while travelling outside mainland China. You can find this extension on Chrome Web Store at [http://uku.im/chrome](http://uku.im/chrome).
 
 ## Disclaimer