Place module list on its own line

The markup emitted by Jbuilder treated module lists as inline elements
that can appear inside a line. However, neither ocamldoc nor odoc render
module lists as inline elements. They are instead block elements, that
are laid out vertically, like lists or paragraphs. Correspondingly, odoc
now rejects inline module list markup.

A side effect of the (rejected) misconception is that there was a stray
period appearing on its own line in every module list generated by
Jbuilder. This is now fixed.

src/odoc.ml

@@ -84,7 +84,7 @@ let lib_index sctx ~odoc ~dir ~(lib : Library.t) ~lib_public_name ~doc_dir ~modu
             sprintf
               "%s\n\
                {2 Library %s}\n\
-               This library exposes the following toplevel modules: {!modules:%s}."
+               This library exposes the following toplevel modules:\n{!modules:%s}"
               header
               lib_public_name
               (String_map.keys modules |> String.concat ~sep:" "))))