title: Formatting numbers with commas in D3
body: <p>When I create a chart with D3 the axis labels have commas in them to delimit thousands, millions, etc.</p>
  
  <p>Is there a D3 function that I can call passing it a number and getting back a string formatted with commas like used in the axis?  It would be the equivalent of this C#: <code>x.ToString("0,000")</code>.</p>
  
  <p>I know there exist libraries to do formatting like this, but I'd like to avoid including additional libraries.  I'm using D3 already, so if there is an API in there I can use that would be great.</p>