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.
Replaced boost/ with msgpack/ and BOOST with MSGPACK in Boost.Preprocessor files.
Renamed existing macron in versioning.hpp to avoid confict with MSGPACK_PP_*.
Removed MSGPACK_USE_BOOST requirement from MSGPACK_DEFINE_MAP.