title: Using In-App billing to purchase full version of the game
body: <p>I want to integrate In-App billing in the free version of my game, to allow user purchase the full version from the free version itself.
  I already got In-App billing working and I could easily make additional items in game available.
  The problem is I don't know what to do to start download of full version of the game and to actually purchase the full version from the market.</p>