I added an options screen, which replaces the akward "Subscribe" window which would popup when you'd click subscribe. This way, you get sent straight to your RSS reader, which again saves you a few clicks. I also added the option for custom reader URLs, for RSS readers not supported out of the box (this is especially handy for selfhosted FreshRSS or Miniflux instances).

I also reformatted the codebase using prettier :P

I added a nice preview for unstyled RSS feeds using XSLT stylesheets. The preview also has a subscribe button, that works the same way the toolbar icon does.