title: Active Model Serializer with different serializer for each model
body: <p>I'm using ActiveModelSerializer 0.10. I have a collection of <code>Account</code>s that I want to serialize. Is there some way to set a specific serializer for each model in the collection? I want my controller to return something like this:</p>
  
  <pre><code>{"accounts":
    [
      {"type":"Group","groupname":"A group","internal_info":"Sensitive info"},
      {"type":"User","first_name":"Bob","last_name":"Smith","internal_info":"Sensitive info"}
    ]
  }
  </code></pre>
  
  <p>My API is divided into two parts: a user API and an admin API. The user API uses the standard serializers which ActiveModelSerializer finds automatically. Something like this</p>
  
  <pre><code>render json: @accounts
  </code></pre>
  
  <p>would return this (note that sensitive information is not included):</p>
  
  <pre><code>{"accounts":
    [
      {"type":"Group","groupname":"A group"},
      {"type":"User","first_name":"Bob","last_name":"Smith"}
    ]
  }
  </code></pre>
  
  <p>The admin API uses custom serializers (they includes more details, for instance the <code>internal_info</code>). How can I render such a collection in my admin API? I know I can use</p>
  
  <pre><code>render json: @accounts, each_serializer: Admin::AccountSerializer
  </code></pre>
  
  <p>which works perfectly in most cases, but in this particular case I have two types of <code>Account</code>s. Can I somehow use <code>Admin::Account::GroupSerializer</code> for <code>Group</code> objects in the collection and <code>Admin::Accounts::UserSerializer</code> for <code>User</code> objects in the collection?</p>