title: Add leading and trailing zeroes to a string/label in swift
body: <p>In swift I know how to set the number of digits after the decimal point when converting a double to a string:</p>
  
  <pre><code>String(format: "%0.2f", someDouble)
  </code></pre>
  
  <p>Similarly I know how to set the number of digits before the decimal point:</p>
  
  <pre><code>String(format: "%02d", someDouble)
  </code></pre>
  
  <p>But how can I do both?</p>
  
  <p>I want the string to always have a 00.00 format. </p>
  
  <p>Thanks</p>