title: Change capstyle for errorbars in matplotlib
body: <p>I would like to set the capstyle for the vertical lines of an error bar to 'round'. For example, the following code produces some points with errorbars:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  
  fig, ax = plt.subplots()
  plt.plot([1,2,3], [2,3,4], marker='o', linestyle='None')
  plt.errorbar([1,2,3], [2,3,4], yerr=[1,1,1], fmt=None, linewidth=3, capsize=0)
  plt.xlim([0,4])
  plt.show()
  </code></pre>
  
  <p>For normal lines, I can set the cap style in the <code>rcParams</code> using this:</p>
  
  <pre><code>plt.rcParams['lines.dash_capstyle'] = 'round'
  </code></pre>
  
  <p>and I also found some nice examples how to get round capstyles for ticks:</p>
  
  <pre><code>for i in ax.xaxis.get_ticklines(): i._marker._capstyle = 'round'
  </code></pre>
  
  <p>but I am not able to find a similar way for the errorbars.</p>