fix parser to work well without any instanciation

`parse_line()` and `parse_file()` should be more casual function.

```perl
Text::LTSV->parse_line($str)
#works as same as "Text::LTSV->new->parse_line($str)"

Text::LTSV->parse_file($file)
#syntax sugar for Text::LTSV->new->parse_file($file)
```

Fixed version of `parse_line()` is not same with `Text::LTSV->new->parse_line($str)` correctly. It's because less cost  for non-`bless()`.