add some wide/utf8 convertion methods
add following methods:
size_t int_to_wide(int c, wchar_t * res, size_t max_buf_len);
template<typename StreamIteratorType>
bool utf8_to_wide(StreamIteratorType & iterator_in, const StreamIteratorType & iterator_end, wchar_t * out_buffer, size_t max_buffer_len, int mode = 1, bool * was_buffer_sufficient_large = nullptr);
template<typename StreamType>
bool utf8_to_wide(const StreamType & stream, wchar_t * out_buffer, size_t max_buffer_len, bool * was_buffer_sufficient_large = nullptr, int mode = 1);
template<typename StreamType>
bool wide_stream_to_utf8(StreamType & buffer, char * utf8, std::size_t max_buffer_size, bool * was_buffer_sufficient_large = nullptr, int mode = 1);