doxy: enable TYPEDEF_HIDES_STRUCT

This means that typedef struct SomeStruct {...} SomeStruct will only be
documented as SomeStruct in the doxy, without a pointless entry in the
typedefs list.

doc/Doxyfile

@@ -277,7 +277,7 @@ SUBGROUPING            = YES
 # be useful for C code in case the coding convention dictates that all compound
 # types are typedef'ed and only the typedef is referenced, never the tag name.
 
-TYPEDEF_HIDES_STRUCT   = NO
+TYPEDEF_HIDES_STRUCT   = YES
 
 # The SYMBOL_CACHE_SIZE determines the size of the internal cache use to
 # determine which symbols to keep in memory and which to flush to disk.