Support std::byte* where only char* is currently supported

[drrlvn]

For example sbuffer::write() should accept const std::byte * in addition to const char *.

[redboltz]

The core of msgpack-c depends on char. For example, https://github.com/msgpack/msgpack-c/blob/master/include/msgpack/v2/parse.hpp#L240

One way to support std::byte is replace xxx with basic_xxx<CharType> all part of msgpack-c. And provide typedef basic_xxx<char> xxx;. Then user can use basic_xxx<std::byte>. It's very big change. I don't think that replace is practical approach.