title: Use an existing key by another one in app.config
body: <p>I want to know if there is a way to use a key in the value of another one.
  For example i have the following config:</p>
  
  <pre><code>&lt;appSettings&gt;   
  &lt;add key="CustomerAdress" value="http://localhost/SD/Service/CustomerS.svc/ComputeCust"/&gt;
  &lt;/appSetting&gt;
  </code></pre>
  
  <p>I want to create a key that contains the first part of the uri : <a href="http://localhost/SD/Servic" rel="nofollow">http://localhost/SD/Servic</a></p>
  
  <pre><code>&lt;add key="SdServices" value="http://localhost/SD/Service"/&gt;
  </code></pre>
  
  <p>and use the key "SdServices" as follows :</p>
  
  <pre><code>&lt;add key="CustomerAdress" value="SdServices/CustomerS.svc/ComputeCust"/&gt;
  </code></pre>
  
  <p>Thank you.</p>