Conform with The Atom Syndication Format (RFC 4287) #181
Description
Conform with The Atom Syndication Format (RFC 4287), and only add new elements that RFC 4287 does not provide.
This is essential for the future of interoperability.
For example, some say that JSON Feed should be utilized for Nostr @nostr-protocol instead of its own format, and in future, Nostr might have JSON Feed, and in the further future, it might have The Atom Syndication Format, or even both.
Hence, I deem it to be assential to conform with RFC 4287 more than less, including changing "tag" to "category", even though I agree that "tag" or "label" be a better name that "category".