title: WooCommerce Subscriptions - Action on initial payment
body: <p>I am using the WooCommerce subscriptions plugin, in particular the <code>woocommerce_subscription_payment_complete</code> function.</p>
  
  <p>I am using it like this:</p>
  
  <pre><code>add_action('woocommerce_subscription_payment_complete','subscription_created');
  function subscription_created($subscription) {
      echo 'Run when subscription payment is complete';
  }
  </code></pre>
  
  <p>This works, but it also fires when a renewal payment completes.  Does anybody know of a way to determine if the payment was for an initial subscription payment rather than a renewal?</p>