doxy: don't sort struct members alphabetically

The declaration order is more meanigful in most cases.

doc/Doxyfile

@@ -409,7 +409,7 @@ INLINE_INFO            = YES
 # alphabetically by member name. If set to NO the members will appear in
 # declaration order.
 
-SORT_MEMBER_DOCS       = YES
+SORT_MEMBER_DOCS       = NO
 
 # If the SORT_BRIEF_DOCS tag is set to YES then doxygen will sort the
 # brief documentation of file, namespace and class members alphabetically