Adding sub links to doxygen_crawl file.

Adding [possibility to do some more link checking as there is also a problem with the links from addIndexItem:
```
file:///.../html/namespaceito33_1_1finance.html
 Lines: 13, 39, 42
  Code: 200 (no message)
 To do: Some of the links to this resource point to broken URI fragments
        (such as index.html#fragment).
The following fragments need to be fixed:
        a522cd9d32a68eabce080861331e10259a8ba18c9e30fe35e3f041b6ee1453d413      Line: 42
```

src/sitemap.cpp

@@ -164,3 +164,59 @@ void Crawlmap::addContentsItem(bool, const QCString &, const QCString &,
     p->crawlLinks.insert(link);
   }
 }
+
+static QCString makeFileName(const QCString & withoutExtension)
+{
+  QCString result=withoutExtension;
+  if (!result.isEmpty())
+  {
+    if (result.at(0)=='!') // relative URL -> strip marker
+    {
+      result=result.mid(1);
+    }
+    else // add specified HTML extension
+    {
+      addHtmlExtensionIfMissing(result);
+    }
+  }
+  return result;
+}
+
+static QCString makeRef(const QCString & withoutExtension, const QCString & anchor)
+{
+  if (withoutExtension.isEmpty()) return QCString();
+  QCString result = makeFileName(withoutExtension);
+  if (anchor.isEmpty()) return result;
+  return result+"#"+anchor;
+}
+void Crawlmap::addIndexItem(const Definition *context, const MemberDef *md,
+                            const QCString &sectionAnchor, const QCString &title)
+{
+  if (md) // member
+  {
+    bool separateMemberPages = Config_getBool(SEPARATE_MEMBER_PAGES);
+    if (context==nullptr) // global member
+    {
+      if (md->getGroupDef())
+        context = md->getGroupDef();
+      else if (md->getFileDef())
+        context = md->getFileDef();
+    }
+    if (context==nullptr) return; // should not happen
+    QCString cfname  = md->getOutputFileBase();
+    //QCString argStr  = md->argsString();
+    QCString cfiname = context->getOutputFileBase();
+    QCString contRef = separateMemberPages ? cfname : cfiname;
+    QCString anchor  = !sectionAnchor.isEmpty() ? sectionAnchor : md->anchor();
+    QCString ref;
+
+    ref = makeRef(contRef, anchor);
+    p->crawlLinks.insert(ref.str());
+  }
+  else if (context) // container
+  {
+    QCString contRef = context->getOutputFileBase();
+    QCString ref = makeRef(contRef,sectionAnchor);
+    p->crawlLinks.insert(ref.str());
+  }
+}

src/sitemap.h

@@ -65,7 +65,7 @@ class Crawlmap
                          bool separateIndex,bool addToNavIndex,
                          const Definition *def);
     void addIndexItem(const Definition *context, const MemberDef *md,
-                      const QCString &sectionAnchor, const QCString &title){}
+                      const QCString &sectionAnchor, const QCString &title);
     void addIndexFile(const QCString & name);
     void addImageFile(const QCString & name){}
     void addStyleSheetFile(const QCString & name){}