Method iterator_input_adapter

include/jwt/json/json.hpp:4848–4849

    using char_type = typename std::iterator_traits<IteratorType>::value_type;

    iterator_input_adapter(IteratorType first, IteratorType last)
        : current(std::move(first)), end(std::move(last)) {}

    typename std::char_traits<char_type>::int_type get_character()
    {