These template functions convert text in a given character set to unicode characters. beg_iter and
end_iter define an input sequence of chars in the charset character set. They get converted to unicode
characters. output_iter is an output iterator that convert() iterates over char32_ts. convert() returns
the value of the output iterator after iterating over the converted character sequence. errflag, passed
by reference, gets set to true if some character could not be converted to unicode, from the specified
character set, and false if the conversion completed without errors.
An overloaded convert() puts the unicode character sequence into a vector of char32_ts, instead of an
output sequence, and returned the error flag. Finally, a single std::string specifies the character
string, instead of a beginning and an ending iterator, and returns a std::pair with the converted unicode
text in a vector, and the error flag.