Drops the URL fragment from links that address a `programs.foo` or
`services.foo` page. Such a path names a module rather than an option,
so the page carries no matching anchor and the fragment pointed nowhere.
Option paths keep their fragment, including the single-segment options
`lib`, `specialisation` and `uninstall`, whose name equals their page
path.
Moves the anchor handling that convert-markup.py and render-options.py
had in common into a new option_links module imported by both. The
derivations therefore pass the mdbook directory instead of a single
script file, so the import resolves.
