Allow using stdin

[Philipp A.]

Your test file_exists('php://stdin') returns FALSE, and file_get_contents doesn’t work with /dev/stdin or -. I suggest that you

1. get rid of the check (file_get_contents will complain with a better message anyway if it can’t read the file), and
2. do if ($options['input'] === '-') $options['input'] = 'php://stdin'; for a more natural command line interface