Documentation|API: Tweaked Doxygen config

Something is not working quite right with Doxygen's macro expansion.

doomsday/libdeng2/api2.doxy

@@ -9,7 +9,12 @@ OUTPUT_DIRECTORY        = ../apidoc/api2/
 INPUT                   = include src
 FILE_PATTERNS           = *
 EXCLUDE_PATTERNS        = .DS_Store
-PREDEFINED              = __cplusplus __DENG2__ 
+PREDEFINED              = __cplusplus __DENG2__ \
+                          "DENG2_PIMPL(ClassName)=typedef ClassName Public; struct ClassName::Instance : public de::Private<ClassName>" \
+                          "DENG2_PIMPL_NOREF(C)=struct C::Instance : public de::IPrivate" \
+                          "DENG2_PRIVATE(Var)=struct Instance; Instance *Var;" \
+                          "DENG2_ERROR(N)=class N : public de::Error {};" \
+                          "DENG2_SUB_ERROR(B,N)=class N : public B {};"                           
 
 INCLUDED_BY_GRAPH       = NO
 COLLABORATION_GRAPH     = NO