title: How to add data to a dict-like Item Field using ItemLoaders?
body: <p>I'm using Scrapy's XPathItemLoader, but it's api only documents adding values to an Item Field, but not any deeper :( I mean:</p>
  
  <pre><code>def parse_item(self, response):
      loader = XPathItemLoader(response=response)
      loader.add_xpath('name', '//h1')
  </code></pre>
  
  <p>Will add the values found by the xpath to <code>Item.name</code>, but how to add them to <code>Item.profile['name']</code>?</p>