title: How to inject constructor argument from config file with Unity
body: <p>Imagine we have a class</p>
  
  <pre><code>public class MyClass
  {
      private string _val;
      public MyClass(string val) 
      {
           _val = val;
      }
  }
  </code></pre>
  
  <p>and app.config (or web.config)</p>
  
  <pre><code>&lt;appSettings&gt;
      &lt;add key="value" value="some value" /&gt;
  &lt;/appSettings&gt;
  </code></pre>
  
  <p>Is there way to register type MyClass in Unity container and point Unity to inject value for val constructor parameter from config file?</p>