Lint checking PHP code samples in README.md

lint.php

<?php

$contents = file_get_contents(__DIR__ . '/README.md');

$start = 0;
while (true) {
    $start = strpos($contents, '```php', $start);
    if ($start === false) {
        break;
    }
    $end = strpos($contents, '```', $start + 1);
    $code = substr($contents, $start, $end - $start);

    $file = tempnam(sys_get_temp_dir(), microtime(true) * 10000);
    file_put_contents($file, $code);
    $output = shell_exec("php -l $file");
    if (strpos($output, 'No syntax errors detected') === false) {
        $line = substr_count($contents, "\n", 0, $start) + 1;
        echo $line . ':' . PHP_EOL . $output . PHP_EOL . PHP_EOL;
    }
    unlink($file);

    $start = $end + 1;
}