Error positions should be reported in characters not in bytes

[na4zagin3]

Issue

Error positions are reported in bytes while it should be in characters.

Example

Input

@require: stdjabook

document (|
  title = {test};
  author = {test};
  show-title = false;
  show-toc = false;
|) '< +p {
あ;
}
>

Current Output

 ---- ---- ---- ----
  target file: 'output.pdf'
  dump file: 'input.satysfi-aux' (will be created)
  parsing 'input.saty' ...
! [Syntax Error at Lexer] at "input.saty", line 9, characters 3-4:
    illegal token ';' in an inline text area

Expected Output

 ---- ---- ---- ----
  target file: 'output.pdf'
  dump file: 'input.satysfi-aux' (will be created)
  parsing 'input.saty' ...
! [Syntax Error at Lexer] at "input.saty", line 9, characters 2-2:
    illegal token ';' in an inline text area

Related Issues

Reported at pickoba/satysfi-workshop#5

Related GH Issue: #308