More cleanup on headers/source for doxygen

- it also found things like size_t instead of size_type in fileName class

src/OpenFOAM/db/functionObject/functionObject.H

@@ -28,6 +28,9 @@ Class
 Description
     Abstract base-class for Time/database function objects.
 
+See Also
+    Foam::OutputFilterFunctionObject
+
 SourceFiles
     functionObject.C