Removed MSGPACK_API_VERSION_NAMESPACE(v1) from doxygen build.
It seems that Doxygen cannot parse a complicated macro such as MSGPACK_API_VERSION_NAMESPACE.
Added EXTRACT_ALL=YES to Doxyfle.
Added INPUT configuration variable that is point to include directory to Doxyfile.
Even if ref_size is given on vrefbuffer's constructor, the minimum size of vrefbuffer::ref_buffer is 10.
Because int64, uint64, and double's msgpack expression size equals 9, and those buffer is allocated on the stack internally.