Rename struct.pack_to to struct.pack_into as changed in revision 46642.

Doc/whatsnew/whatsnew25.tex

@@ -1653,7 +1653,7 @@ year, number, name = s.unpack(data)
 \end{verbatim}
 
 You can also pack and unpack data to and from buffer objects directly
-using the \method{pack_to(\var{buffer}, \var{offset}, \var{v1},
+using the \method{pack_into(\var{buffer}, \var{offset}, \var{v1},
 \var{v2}, ...)} and \method{unpack_from(\var{buffer}, \var{offset})}
 methods.  This lets you store data directly into an array or a
 memory-mapped file.