title: Formatting objects in chai.expect errors
body: <p>When test fails, where I'm comparing two objects using <code>expect(x).to.deep.equal(y)</code>, I'd like to see the actual values in my browser test report. Instead, I see something like this:</p>
  
  <pre><code>AssertionError: expected { Object (x, y, ...) } to deeply equal { Object (x, y, ...) }
  </code></pre>
  
  <p>So it doesn't really show anything useful.</p>
  
  <p>Is there a way to customize how chai.js formats these objects?</p>