docs: Added release notes for Google APIs System Image v4.

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  <p><a href="#" onclick="return toggleContent(this)">

    <img src="{@docRoot}assets/images/triangle-opened.png"

class="toggle-content-img" alt="" />Revision 4</a> <em>(March 2014)</em>

  </p>

  <div class="toggle-content-toggleme">

    <p>This release includes

    <a href="{@docRoot}google/play-services/index.html">Google Play services</a> version 4.3,

    allowing you to test your application in an emulator using the latest Google Play services.</p>

  </div>

</div>

<div class="toggle-content closed">

  <p><a href="#" onclick="return toggleContent(this)">

    <img src="{@docRoot}assets/images/triangle-closed.png"

class="toggle-content-img" alt="" />Revision 3</a> <em>(February 2014)</em>

  </p>