message: __has_include to #include <string_view>
  suggestion
diff: -#if __cplusplus < 201703L
  +#if __cplusplus >= 201703L || defined(__has_include) && __has_include(<string_view>)
  +#include <string_view>
  +#else
  #define STX_NAMESPACE_NAME std
  #include "string_view.hpp"
  -#else
  -#include <string_view>
  #endif
  