Make custom_display_name work for project-level items

This lets users customize the way module/topic/file/etc names are shown.

ldoc/html.lua

@@ -176,6 +176,11 @@ function ldoc.source_ref (fun)
    end
 
    function ldoc.default_display_name(item)
+      -- Project-level items:
+      if doc.project_level(item.type) then
+        return ldoc.module_name(item)
+      end
+      -- Module-level items:
       local name = item.display_name or item.name
       if item.type == 'function' or item.type == 'lfunction' then
          if not ldoc.no_space_before_args then

ldoc/html/ldoc_ltp.lua

@@ -66,7 +66,7 @@ return [==[
 #  if ldoc.allowed_in_contents(type,module) then
 <h2>$(kind)</h2>
 <ul class="$(kind=='Topics' and '' or 'nowrap'">
-#  for mod in mods() do local name = ldoc.module_name(mod)
+#  for mod in mods() do local name = display_name(mod)
 #   if mod.name == this_mod then
   <li><strong>$(name)</strong></li>
 #   else