title: Reshape Pandas DataFrame to a Series with columns prefixed with indices
body: <p>Say I have a Pandas DataFrame like this one:</p>
  <pre><code>      A    B
  idx1  1    3
  idx2  2    4
  </code></pre>
  <p>Is there a pandas function that converts this table to something like this?</p>
  <pre><code>A_idx1  A_idx2 B_idx1 B_idx
  1       2      3      4
  </code></pre>