Add an option to sort object keys

[curvedmark]

This could be helpful when using jsDump to show object diffs.

If you find the opportunity, please update this package on npm. I sent a pull request to mocha (https://github.com/visionmedia/mocha/pull/589) which does object diff and can benefit from this feature.

Thanks.

[curvedmark]

Also fixed a small bug for node.