title: Capistrano 3 pulling command line arguments
body: <p>I'm in the process of upgrading from Capistrano 2 to Capistrano 3. In Cap 2 I was using the following to take a command line argument as the branch name (otherwise default to <code>master</code>)</p>
  
  <pre><code>set :branch, fetch(:branch, "master")
  </code></pre>
  
  <p>If I called <code>cap deploy</code> it would deploy the master branch. But it also let me do something like this:</p>
  
  <pre><code>cap deploy -S branch=foo
  </code></pre>
  
  <p>Which would deploy the <code>foo</code> branch.</p>
  
  <p>Now, in Capistrano 3, if I try to run the above I get an error: <code>invalid option: -S</code>.</p>
  
  <p>What's the proper way to pass an argument via the command line now?</p>