title: how to customize devise error messages with classes
body: <p>im using twitters bootstrap alert messages. in my application.html.erb I have...</p>
  
  <pre><code>            &lt;% flash.each do |key, value| %&gt;
                  &lt;div class="alert alert-&lt;%=key%&gt;"&gt;
                      &lt;a class="close" data-dismiss="alert"&gt;×&lt;/a&gt;
                      &lt;%= value %&gt;
                  &lt;/div&gt;
             &lt;% end %&gt;
  </code></pre>
  
  <p>normally when I want to do a flash message, I would write something like</p>
  
  <pre><code>flash[:success] = "Profile updated"
  </code></pre>
  
  <p>however im not sure how I can give the devise error messages a key and value pair. I looked into the devise.en.yml but can't seem to associate the message with a key ie :success, :error etc.
  could someone help? thanks!</p>