Add the ASS sub document and the ASS tree

Also add views for the ASS tree in read only mode for now

src/Lib/Ass/Ass.hh

 #ifndef VIVY_ASS_ASS_H
 #define VIVY_ASS_ASS_H
 
-#include "Char.hh"
 #include "Line.hh"
 #include "Syl.hh"
 #include "Style.hh"
+#include "AssPrivate.hh"
 #include "AssFactory.hh"
 #include "StyleProperties.hh"
 #include <memory.h>
 
-namespace Vivy::Ass
-{
-using StylePtr = AssFactory::StylePtr;
-using LinePtr  = AssFactory::LinePtr;
-
-using StyleWeakPtr = AssFactory::StyleWeakPtr;
-using LineWeakPtr  = AssFactory::LineWeakPtr;
-}
-
 #endif // VIVY_ASS_ASS_H