title: rails: yml merging
body: <p>Say I have a yml file for my rails configuration...</p>
  
  <p><strong>settings.yml</strong></p>
  
  <pre><code>defaults: &amp;defaults
    interceptor_email: robot@wearemanalive.com
  
  development:
    &lt;&lt;: *defaults
  
  test:
    &lt;&lt;: *defaults
  
  production:
    &lt;&lt;: *defaults
  </code></pre>
  
  <p>and I want to have another yml file that is NOT included in version control that each developer maintains locally...</p>
  
  <p><strong>user_settings.yml</strong></p>
  
  <pre><code>development:
    interceptor_email: userfoo@domain.com
  </code></pre>
  
  <p>How can I merge these keys?  I am processing my yml files with esb, so that is also an option. Just having trouble figuring out how to do it.  I have it setup so keys fallback to the defaults if a key is missing for my environments.</p>