- Enhance CMakeLists.txt files.
- Move to Boost Test from Google Test to support pre-C++11 compilers.
- Add more configurations on CI matrix builds.
- Other minor fixes
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.