To remove boost dependency, `-DMSGPACK_USE_BOOST=OFF` for cmake.
By default, `-DMSGPACK_USE_BOOST` is `ON`.
NOTE: In order to build tests `-DMSGPACK_USE_BOOST=ON` is required.
For C++ compiler, the option `-DMSGPACK_NO_BOOST` is required to remove
boost.
- 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.
