MSVC CLI defined their own nullptr and provides for __nullptr for standard C++11.
https://msdn.microsoft.com/en-us/library/4ex65770.aspx
msgpack-c introduce MSGPACK_NULLPTR for internal use, it is defined as __nullptr only if compiled on C++ CLI otherwise defined as nullptr.
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.
Added a referenced parameter to msgpack::unpack() and msgpack::unpacker::next().
msgpack::unpacked is a kind of handler that holds msgpack::object and msgpack::zone, so the size of msgpack::unpacked should be small. There is no reason to have referenced in msgpack::unpacked. msgpack user can get the same information using msgpack::unpack() and msgpack::unpacker::next().
