title: Shared session vs. session with default configuration
body: <p>What are the differences between the two <code>session</code> objects created in these two different ways:</p>
  
  <pre><code>NSURLSession *session = [NSURLSession sharedSession];
  </code></pre>
  
  <p>and</p>
  
  <pre><code>NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
  NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration];
  </code></pre>