title: Scrapy ordering guarantees
body: <p>Is there an ordering guarantees for items emitted by spider and processed by pipelines.</p>
  
  <p>In other words, if my spider yields items: <code>item1, item2, item3</code> from it's <code>parse</code> method, is there a guarantee that my pipeline will process items in the same order (<code>item1, item2, item3</code>)?</p>