title: selecting rows based on multiple column values in pandas dataframe
body: <p>I have a <code>pandas</code> <code>DataFrame</code> <code>df</code>:</p>
  
  <pre><code>import pandas as pd
  
  data = {"Name": ["AAAA", "BBBB"],
          "C1": [25, 12],
          "C2": [2, 1],
          "C3": [1, 10]}
  
  df = pd.DataFrame(data)
  df.set_index("Name")
  </code></pre>
  
  <p>which looks like this when printed (for reference):</p>
  
  <pre><code>      C1  C2  C3
  Name            
  AAAA  25   2   1
  BBBB  12   1  10
  </code></pre>
  
  <p>I would like to choose rows for which <code>C1</code>, <code>C2</code> and <code>C3</code> have values between <code>0</code> and <code>20</code>.</p>
  
  <p>Can you suggest an elegant way to select those rows?</p>