title: How do I add a prefix to each key in a hash?
body: <p>I have the following keys in my hash: </p>
  
  <pre><code>address, postcode
  </code></pre>
  
  <p>I want to add the "shipping_" prefix to each of them so they would become:</p>
  
  <pre><code>shipping_address, shipping_postcode
  </code></pre>
  
  <p>instead. How can I do this?</p>