title: Create new column (pandas dataframe) when duplicate ids have a payment date
body: <p>I have a pandas dataframe:</p>
  <pre><code>pd.DataFrame({'id': [1, 1, 2, 2, 3, 3],
           'payment_count': 1, 2, 1, 2, 1, 2,
           'payment_date': ['2/2/2020', '4/6/2020', '3/20/2020', '3/29/2020', '5/1/2020', '5/30/2020']})
  </code></pre>
  <p>I want to take max('payment_count') by each 'id' and create a new column with the associated 'payment_date'. Desired output:</p>
  <pre><code>pd.DataFrame({'id': [1, 2, 3],
           'payment_date_1': ['2/2/2020', '3/20/2020', '5/1/2020'],
           'payment_date_2': ['4/6/2020', '3/29/2020', '5/30/2020']})
  </code></pre>