Clean up package.json

Reformats and cleans up `package.json` per these docs:

- https://www.npmjs.org/doc/json.html
- http://package.json.nodejitsu.com

Additionally, our version of  `async` is substantially out of date, the most recent release is `0.7.0`. Perhaps worth looking into whether or not we're still compatible, and updating if so?

I think I got all the emails in `contributors` right, please let me know if I didn't.