Method is_object

example/json.hpp:293–293

        bool is_number() const noexcept { return kind() == value_kind::number; }
        bool is_string() const noexcept { return kind() == value_kind::string; }
        bool is_object() const noexcept { return kind() == value_kind::object; }
        bool is_array() const noexcept { return kind() == value_kind::array; }

        bool operator==(value const & rhs) const noexcept