Fix utf-8 character writing

[skjerns]

There seems to be a problem with writing uft8 chars, see #275

The problem was that chinese utf chars are multi byte encoded, however, the C extension sanitized all byte chars that are below value 32 (control chars). for multi byte, that is actually valid printable unicode. Simply removing this fixes the issue.

for(i=0; ; i++) {
  if(list_annot->annotation[i] == 0) {
    break;
  }
  if(list_annot->annotation[i] < 32) {
    list_annot->annotation[i] = '.';
  }
}

fixes #275