title: Support library version
body: <p>I try to inject support libraries into my Android Studio project.</p>
  
  <p>If I try anything lower than 20 it says: 
  library should not use a lower version then targetSdk version.</p>
  
  <p>If I use <code>compile 'com.android.support:support-v4:20'</code> I get:
  Failed to find: com.android.support:support-v4:20</p>
  
  <p>If I use   <code>compile 'com.android.support:support-v7:20.0.+'</code> I get:
  Avoid using + in version numbers, can lead to unpredictable and unrepeatable builds.</p>
  
  <p>So the simple question is:
  where can I find up-to-date, ready to use, version numbers that Do work? </p>