2.0.0: OAuth 2.0 login for creating new feeds

As of the v2.0.0 release of this project, only users who are authenticated with a particular OAuth server can create feeds. Any federated user can still read the feeds. I implemented this because running this service in the open invited thousands of spammers to create feeds and overwhelm the service. With this new model, you can run this as an added bonus for people in a community like a Mastodon server, and as the person running it you are taking on only the moderation burden of the users you are already responsible for on your federated server.

So the idea here is: you run a federated server like Mastodon or Pleroma that offers OAuth 2.0 identity services. You set up this software to run somewhere and point it at the federated OAuth 2.0 provider. Now anybody with an account on that federated server can log in to this RSS to ActivityPub converter and create new feeds. But people without accounts on your server cannot.

There are details in README.md about how to set this up.