feat: Programmatic pages

[kevinrenskers]

• It's currently not very easy to render the homepage with a specific html template, because when you leave the folder empty, it processes ALL markdown, recursive. It's not clear how to make a processing step that only processes the homepage, without also processing other pages (such as the about page). Maybe a filter that ignores everything except /index.md, but is that obvious enough. We can do better.

• It's currently not clear to how render a template to a HTML page wihhout there being an Item involved (like a markdown file). Let's say I have an HTML template render404 and I want to render this to /404.html. What kind of register step would make that possible? The new programmatic step with the fetch method that just returns a dummy Item?

The solution: a new createPage step.

try await Saga(input: "content", output: "deploy")
  .register(
    folder: "articles",
    metadata: ArticleMetadata.self,
    readers: [.parsleyMarkdownReader],
    writers: [
      .itemWriter(swim(renderArticle)),
      .listWriter(swim(renderArticles)),
    ]
  )
  .createPage("index.html", using: swim(renderHome))
  .createPage("404.html", using: swim(render404))
  .run()

I also deprecated the staticFiles step. run now just always copies the static files.