add class hierarchy diagrams

docs/Doxyfile.in

@@ -2032,7 +2032,7 @@ HIDE_UNDOC_RELATIONS   = YES
 # set to NO
 # The default value is: NO.
 
-HAVE_DOT               = NO
+HAVE_DOT               = YES
 
 # The DOT_NUM_THREADS specifies the number of dot invocations doxygen is allowed
 # to run in parallel. When set to 0 doxygen will base this on the number of
@@ -2098,7 +2098,7 @@ GROUP_GRAPHS           = YES
 # The default value is: NO.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-UML_LOOK               = NO
+UML_LOOK               = YES
 
 # If the UML_LOOK tag is enabled, the fields and methods are shown inside the
 # class node. If there are many fields or methods and many nodes the graph may