title: google adwords api + getting all keywords
body: <p>I'm using the google adwords api, I can retrieve all campaigns, group ads, ads,
  but I have no idea on how to retrieve keywords related to an "group ads".
  In the google adwords interface, when we select a group ads, we have two tabs, one for ads related to that group ads, and the second for keywords.
  but programatily, right now I can only retrieve ads.
  I'm using PHP, if some one knew how to do that in php or others programming languages or even a soap call.</p>