Meta: Convert new help page link styles for the man page website

The special URL links (help://man) and the application opening links now
work on the man page website. While the page links are translated
correctly, the application launch can't be implemented. For this reason,
an explanatory error page is shown instead.

Meta/Websites/man.serenityos.org/cant-run-application.md

@@ -0,0 +1,5 @@
+# Sorry :^(
+
+This is a link to open the application directly, but that only works in SerenityOS.
+
+[Go back to main page](index.html)

Meta/build-manpages-website.sh

@@ -97,6 +97,11 @@ pandoc -f gfm -t html5 -s \
     --metadata title="SerenityOS man pages" \
     -o output/index.html \
     Meta/Websites/man.serenityos.org/index.md
+pandoc -f gfm -t html5 -s \
+    -B Meta/Websites/man.serenityos.org/banner-preamble.inc \
+    --metadata title="Can't run applications" \
+    -o output/cant-run-application.html \
+    Meta/Websites/man.serenityos.org/cant-run-application.md
 
 # Copy pre-made files
 cp Meta/Websites/man.serenityos.org/banner.png output/

Meta/convert-markdown-links.lua

@@ -1,4 +1,5 @@
 function Link(el)
-    el.target = string.gsub(el.target, "%.md", ".html") -- change .md to .html links
+    el.target = string.gsub(el.target, "file:///bin/.*", "../cant-run-application.html")
+    el.target = string.gsub(el.target, "help://man/([^/]*)/(.*)", "../man%1/%2.html")
     return el
 end

Userland/Utilities/markdown-check.cpp

@@ -47,6 +47,7 @@ static bool is_missing_file_acceptable(String const& filename)
         "/man6/index.html",
         "/man7/index.html",
         "/man8/index.html",
+        "index.html",
     };
     for (auto const& suffix : acceptable_missing_files) {
         if (filename.ends_with(suffix))