title: set up expiration for putObject in s3 php sdk
body: <p>This is working codes for creating bucket and putObject:</p>
  
  <pre><code>$bucket = uniqid("php-sdk-sample-", true);
  echo "Creating bucket named {$bucket}\n";
  $result = $client-&gt;createBucket(array(
  'Bucket' =&gt; $bucket
  ));
  // Wait until the bucket is created
  $key = 'hello_world.txt';
  echo "Creating a new object with key {$key}\n";
  $result = $client-&gt;createObject(array(
  'Bucket' =&gt; $bucket,
  'Key'    =&gt; $key,
  'Body'   =&gt; "Hello World!" 
  ));
  </code></pre>
  
  <p>How can I set up expiration date for this just created object ? For ex. I want to see disappear the uploaded file 3 days later. </p>