title: SI-prefix with significant digits but trimming trailing decimal zeros in d3.js
body: <pre><code>d3.format('.2s')( 1234 );    // "1.2k"
  d3.format('.2s')( 1000 );    // "1.0k"
  
  // want
  d3.format('???')( 1234 );    // "1.2k"
  d3.format('???')( 1000 );    // "1k",  NOT "1.0k"
  </code></pre>
  
  <p>Possible to use the same <code>'???'</code> format to get both wanted strings?</p>