Page2RSS replacement. Get content changes for an URL as an Atom feed.
2018-12-26: Registration, sign-in, per-user feeds
2018-12-22: FIX: The latest feed entry is now used to compute the "change summary" when adding a new entry.
2018-12-11: Replaced HtmlAgilityPack with AngleSharp.
2018-12-10: Migrated to .NET Core 2.2 & Visual Studio 2019.
2018-12-09: Initial working version.