title: What does "@aar" means in gradle 'compile' task
body: <p>I'm new in gradle and cannot find any documentation about this feature. </p>
  
  <p>All I noticed is that
  <code>compile 'com.github.asne:asne-vk:0.2.1'</code> caused some manifest merging problems (some grunting abot different minSdkVersions) and that <code>compile 'com.github.asne:asne-vk:0.2.1@aar'</code> works fine.</p>