title: using dictionary as a key in other dictionary
body: <p>I would like to use <code>Dictionary</code> as <code>TKey</code> in another <code>Dictionary</code>. Something similar to python. I tried this but it gives me errors.</p>
  
  <pre><code>Dictionary&lt;Dictionary&lt;string, string&gt;, int&gt; dict = new Dictionary&lt;Dictionary&lt;string,    string&gt;, int&gt;();
  Dictionary&lt;string, string&gt; dict2 = new Dictionary&lt;string, string&gt;();
  dict2["abc"] = "def";
  dict[dict["abc"] = 20;
  </code></pre>