title: Add std::pair with + operator
body: <p>Is there a simple way to make a+b work in the following example:</p>
  
  <pre><code>#include &lt;utility&gt;
  #include &lt;iostream&gt;
  
  int main ()
  {
      std::pair&lt;int, int&gt; a=std::make_pair(1,2);
      std::pair&lt;int, int&gt; b=std::make_pair(3,3);
      std::pair&lt;int, int&gt; c = a+b;
  
      return 0;
  }
  </code></pre>