search: rank older manual page versions lower

Old manual page versions are almost always uninteresting. So let's avoid
showing them first thing.

This feat is accomplished by using the `data-pagefind-weight` attribute
(which affects also the header tags that would usually rank higher in
the search index: the `data-pagefind-weight` attribute extends not only
the tag but all of its child nodes, too, recursively).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

layouts/_default/baseof.html

@@ -102,7 +102,9 @@ <h1>{{ .Params.book.section.cs_number }} {{ .Params.book.chapter.title }} - {{ .
             {{ partial "ref/versions.html" . }}
           </div>
 
-          <div id="main" data-pagefind-body>
+          <!-- older manual page versions are less interesting -->
+          {{ $reduce_weight := (and (isset .Params "docname") (not (isset .Params "latest-changes"))) }}
+          <div id="main"{{ if $reduce_weight }} data-pagefind-weight="0.5"{{ end }} data-pagefind-body>
             {{ .Content }}
           </div>
         </div>

script/update-docs.rb

@@ -395,6 +395,7 @@ def index_doc(filter_tags, doc_list, get_content)
         if page_data["latest-changes"] == version
           FileUtils.mkdir_p(File.dirname(doc_path))
           File.open("#{doc_path}.html", "w") do |out|
+            front_matter["latest-changes"] = version
             front_matter["aliases"] = ["/docs/#{docname}", "/docs/#{docname}.html"]
             out.write("#{front_matter.to_yaml}\n---\n")
             out.write(html)