title: add marker with Google-Maps-for-Rails
body: <p>I was playing with <a href="https://github.com/apneadiving/Google-Maps-for-Rails" rel="nofollow">https://github.com/apneadiving/Google-Maps-for-Rails</a> and
  i'd like to clear all the marker on a map and add a new one at the position clicked by the user on the map, I added the following code in my page</p>
  
  <pre><code>&lt;script type="text/javascript" charset="utf-8"&gt;
  function gmaps4rails_callback() {
     google.maps.event.addListener(Gmaps4Rails.map, 'click', function(object){ 
        alert(object.latLng);
     });
  &lt;/script&gt;
  </code></pre>
  
  <p>And in this way i can see an alert with the lat and long value, now how can i delete the old markers and create a new marker and place it on the map?</p>