- Load and convert the entire input file at once,
  rather than reading string-by-string using fgets().
  This change makes it possible to convert from UCS2, UTF16, UTF32 data.
- Adding the --delimiter command, to treat the specified
  characters as delimiters rather than data to convert.
  Useful in combination with `-f filename` or `-t filename`.
  The delimiter characters are not converted,
  they are copied from the input to the output as is.
- Adding diagnostics with line number and position if:
  * an illegal input byte sequence was found
  * a character cannot be converted to the target character set