title: AutoFixture build collection with unique property
body: <p>Is there any possibility to create a collection with a unique property in <code>AutoFixture</code>? For instance, I would like to create a collection of:</p>
  
  <pre><code>public class Foo {
   public int Id {get; set;}
   public string Name {get;set;}
  }
  </code></pre>
  
  <p>with unique <code>Id</code>. It would look something like this:</p>
  
  <pre><code>var fixture = new Fixture();
  
  fixture
   .Build&lt;Foo&gt;()
   .WithUnique((foo) =&gt; foo.Id)
   .CreateMany(20);
  </code></pre>
  
  <p>I know it is possible to do this through customization, but I think it's quite common scenario so might be <code>AutoFixture</code> has something ready for this?</p>