Now the functions can actually be demonstrated by small examples,
embedded right inside the documentation via:
spreadsheet://example/<page>#<example_name>
Also allows pages to link to each other via the same scheme:
spreadsheet://doc/<page>
In a few places I also simplified a few format strings:
-outln("{} item{}", items, items.size() == 1 ? ' ' : 's');
+outln("{} item(s)", items);
In my opinion this is more readable and in some places it incorrectly
wrote '0 item' which is "fixed" now. In other places the placeholder
space looked weird.
