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.
https://github.com/boostorg/predef.git has been added as a submodule on
external/boost/predef.
In order to avoid macro name conflicts, replaced "BOOST_" with "MSGPACK_"
and "boost/" with "msgpack/" then copy replaced files to include/msgpack.
This process is described in CMakeLists.txt.
Replaced files are included as a part of msgpack-c. So you don't need to
do the converting process each time.
Fixed endian checking logic.
