title: forcing pyYAML to dump consistently
body: <pre><code>In [136]: a = [1,2,3,4,5]
  
  In [137]: print yaml.dump(a)
  [1, 2, 3, 4, 5]
  
  
  In [138]: a = [1,2,3,4,5, [1,2,3]]
  
  In [139]: print yaml.dump(a)
  - 1
  - 2
  - 3
  - 4
  - 5
  - [1, 2, 3]
  </code></pre>
  
  <p>why are the outputs of above two <code>dumps</code> different? Is it possible to force <code>pyYAML</code> to split the <code>list</code> always?</p>