laravel exception handler open emacs file

- laravel:

  - .env: APP_EDITOR=emacs
  - config/app.php: 'editor' => env('APP_EDITOR'),

- https://superuser.com/questions/162092/how-can-i-register-a-custom-protocol-with-xdg

  - https://github.com/charliesome/better_errors/wiki/Link-to-your-editor
  - https://gist.github.com/calas/185186
- https://github.com/filp/whoops/blob/master/docs/Open%20Files%20In%20An%20Editor.md