title: Create new product attribute programmatically in Woocommerce
body: <p>How can I create attributes for WooCommerce from a plugin?
  I find only : </p>
  
  <pre><code>wp_set_object_terms( $object_id, $terms, $taxonomy, $append);
  </code></pre>
  
  <p>From <a href="https://stackoverflow.com/questions/19518878/woocommerce-add-value-to-a-product-attribute">this stack-question</a></p>
  
  <p>But this approach required id of some product. I need to generate some attributes not attached to any products.</p>