How to use marked in WKWebView in AppKit

Issue #429

<!doctype html>
<html>
<head>
  <meta charset="utf-8"/>
  <title>Marked in the browser</title>
</head>
<body>
  <div id="content"></div>
  <script src="https://cdn.jsdelivr.net/npm/marked/marked.min.js"></script>
  <script>
    document.getElementById('content').innerHTML =
      marked(`# Marked in the browser\n\nRendered by **marked**.`);
  </script>
</body>
</html>

Should use back tick instead of ' to deal with multiline string, and escape back tick

let markdown = markdown.replacingOccurrences(of: "`", with: "\\`")
marked(`\(markdown)`);

webView.loadHTMLString(string, baseURL: nil)

For WKWebView to load even local content, need to enable Outgoing connections, and maybe Incoming connections in Sandbox