title: woocommerce_new_order action not returning all order details
body: <p>I'm using the <strong>woocommerce_new_order</strong> action to send order details to a Mailchimp list. </p>
  
  <pre><code>// Add user to mailchimp list
  function add_user_to_mailchimp($order_id) {
      $order = get_post_meta($order_id);
  
      write_log($order);
  
  }
  add_action( 'woocommerce_new_order', 'add_user_to_mailchimp', 1, 1 );
  </code></pre>
  
  <p>An important part to keep in mind is that the user may not necessarily register an account.</p>
  
  <p>The most important part is retrieving the the customers email and sending that through to Mailchimp. I want to achieve this by using</p>
  
  <pre><code>get_post_meta($order_id, 'billing_email', true);
  </code></pre>
  
  <p>but this returns an empty value even if I use '_billing_email'.</p>
  
  <p>When I output the $order in the log I get the following output:</p>
  
  <pre><code>[17-Jan-2017 07:47:35 UTC] Array
  (
       [_wc_customer_order_csv_export_is_exported] =&gt; Array
          (
              [0] =&gt; 0
          )
  
      [_wc_customer_order_csv_export_customer_is_exported] =&gt; Array
          (
              [0] =&gt; 0
          )
  
      [_order_key] =&gt; Array
          (
              [0] =&gt; wc_order_587dcc17ca5f0
          )
  
      [_order_currency] =&gt; Array
          (
              [0] =&gt; ZAR
          )
  
      [_prices_include_tax] =&gt; Array
          (
              [0] =&gt; yes
          )
  
      [_customer_ip_address] =&gt; Array
          (
              [0] =&gt; ::1
          )
  
      [_customer_user_agent] =&gt; Array
          (
              [0] =&gt; Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:50.0) Gecko/20100101 Firefox/50.0
          )
  
      [_customer_user] =&gt; Array
          (
              [0] =&gt; 0
          )
  
      [_created_via] =&gt; Array
          (
              [0] =&gt; checkout
          )
  
      [_cart_hash] =&gt; Array
          (
              [0] =&gt; 4457fd575a37c07e4863ce5610ddb4d2
          )
  
      [_order_version] =&gt; Array
          (
              [0] =&gt; 2.6.4
          )
  
  )
  </code></pre>
  
  <p>Am I perhaps using the wrong action hook? All the values to exist in the database. </p>