title: Difference between android-support-v7-appcompat and android-support-v4
body: <p>I wanted to know the difference between <strong>android-support-v4.jar</strong>
  and <strong>android-support-v7-appcompat.jar</strong>. If I want to add appcompat Action Bar in my application do I need to add both <em>android-support-v7-appcompat.jar</em> and <em>android-support-v4.jar</em> or only <em>android-support-v7-appcompat.jar</em>.</p>
  
  <p>Also, does <em>android-support-v13.jar</em> has appcompat?</p>