Unify page_list entries and page_info cache entries

[noteflakes]

It's really the same thing:

• Add :url/:permalink to page info (that is, load and parse page).
• In page_list, simply get the page_info for each relevant entry in the directory.

So the page_info entry looks like:

{
  path: absolute_file_path,
  ext: file_extension,
  url: page_url,
  title: page_title,
  date: optional_page_date,
  renderer: renderer_proc
}