title: change pandas MultiIndex level by '+1'
body: <p>How to rename MultiIndex level = 0 as mentioned in <a href="http://www.boomboxbooking.de/stackq/stack_pic.png" rel="nofollow noreferrer">this_df</a> like 'ti'->'ti+1'?</p>
  
  <p>this_df contains normalized weights using <em>ti</em> data for computing weighted sums in <em>ti+1</em>.</p>
  
  <pre><code>this_df = pd.read_csv('http://www.boomboxbooking.de/stackq/data.csv', index_col =[0,1], sep=';')
  
  new_index_level_0 = ['t1','t2','t3']
  </code></pre>