msgpack::unpacked is a typedef of the msgpack::object_handle.
I recommend using msgpack::object_handle. It can be used not only
holding unpacked msgpack objects but also msgpack::objects that are
created by any types.
Replaced unpack() APIs in test codes and examples. They used to use old
APIs.
The parameter 'offset' of unpack() function family, not unpacker family, updates only when the function successfully finished.
The parameter 'offset' used to update even if a caller passes insufficient bytes to the unpack() function family.
