Function is_valid

include/utf8cpp/core.h:300–303

    template <typename octet_iterator>
    inline bool is_valid(octet_iterator start, octet_iterator end)
    {
        return (utf8::find_invalid(start, end) == end);
    }

    template <typename octet_iterator>
    inline bool starts_with_bom (octet_iterator it, octet_iterator end)