Class is_valid_json_value

include/jwt-cpp/jwt.h:2420–2427

		template<typename value_type>
		struct is_valid_json_value {
			static constexpr auto value =
				std::is_default_constructible<value_type>::value &&
				std::is_constructible<value_type, const value_type&>::value && // a more generic is_copy_constructible
				std::is_move_constructible<value_type>::value && std::is_assignable<value_type, value_type>::value &&
				std::is_copy_assignable<value_type>::value && std::is_move_assignable<value_type>::value;
			// TODO(prince-chrismc): Stream operators
		};

		// https://stackoverflow.com/a/53967057/8480874
		template<typename T, typename = void>