Rename internal types:

a suffix ending with _ct means confidential type
ans is reserved for M*LIB internal usage.

OPLIST doesn't use the external types
but rather the internal types.
It enables to be independent of the real names
of the external types.
Such external names are planned to be fully customizable
(i.e. the user may define a name that suits its coding style)

README.md

@@ -2227,15 +2227,17 @@ Return true if 'it' references the last element or is no longer valid.
 
 Update the iterator 'it' to the next element.
 
-##### struct name\_pair\_s *name\_ref(name\_it\_t it)
+##### name\_type\_t *name\_ref(name\_it\_t it)
 
-Return a pointer to the pair composed by the key ('key' field) and its value ('value' field).
-'key' element can not be modified.
+Return a pointer to the pair composed by the key ('key' field) and its value ('value' field) if it is not a set,
+to the key type if it is a set.
+'key' element shall not be modified.
 This pointer remains valid until the dictionary is modified by another method.
 
-##### const struct name\_pair\_s *name\_ref(name\_it\_t it)
+##### const name\_type\_t *name\_ref(name\_it\_t it)
 
-Return a constant pointer to the pair composed by the key('key' field)  and its value ('value' field).
+Return a constant pointer to the pair composed by the key ('key' field) and its value ('value' field) if it is not a set,
+to the key type if it is a set.
 This pointer remains valid until the dictionary is modified by another method.
 
 ##### void name\_get\_str(string\_t str, const name\_t dict, bool append)