Fix missing doxygen pages

Set the doxygen option HIDE_UNDOC_CLASSES to NO so even classes
without top level documentation show up. This fixes missing class links
in the documentation.

This problem was introduced when the local doxygen settings were
synchronized with the website doxygen settings:
784fa91
"Update doxygens to be in sync"

Author: c1728p9

doxyfile_options

@@ -484,7 +484,7 @@ HIDE_UNDOC_MEMBERS     = YES
 # has no effect if EXTRACT_ALL is enabled.
 # The default value is: NO.
 
-HIDE_UNDOC_CLASSES     = YES
+HIDE_UNDOC_CLASSES     = NO
 
 # If the HIDE_FRIEND_COMPOUNDS tag is set to YES, doxygen will hide all friend
 # (class|struct|union) declarations. If set to NO, these declarations will be

doxygen_options.json

@@ -25,7 +25,6 @@
     "GENERATE_TESTLIST": "NO",
     "GENERATE_TODOLIST": "NO",
     "HIDE_SCOPE_NAMES": "YES",
-    "HIDE_UNDOC_CLASSES": "YES",
     "HIDE_UNDOC_MEMBERS": "YES",
     "HIDE_FRIEND_COMPOUNDS": "YES",
     "INLINE_INFO": "NO",