Doxygen: Generate call graph and relationships.

It helps code browsing and understanding for new developers.

Utilities/Doxygen/doxyfile.in

@@ -28,6 +28,8 @@ INCLUDED_BY_GRAPH    = YES
 CLASS_DIAGRAMS       = YES
 GENERATE_LEGEND      = YES
 GRAPHICAL_HIERARCHY  = YES
+REFERENCED_BY_RELATION = YES
+REFERENCES_RELATION    = YES
 
 ALLEXTERNALS         = NO
 
@@ -61,7 +63,7 @@ SORT_MEMBER_DOCS     = NO
 DISTRIBUTE_GROUP_DOC = YES
 TAB_SIZE             = 3
 
-FILE_PATTERNS        = *.h *.hxx
+FILE_PATTERNS        = *.h *.hxx *.cxx
 RECURSIVE            = NO
 EXCLUDE_PATTERNS     =