Class not_isspace

src/backward.h:3806–3808

    // there is no find_if_not in C++98, lets do something crappy to
    // workaround.
    struct not_isspace {
        bool operator()(char c) { return !std::isspace(c); }
    };
    // and define this one here because C++98 is not happy with local defined
    // struct passed to template functions, fuuuu.
    struct not_isempty {