Implement `.random()` compliant with `Math.random()`

I implemented the feature I requested.

- `.random()` is just a direct reference to the `.rnd()` method, and it's been documented accordingly (using your documentation format)
- the changelog is updated
- the package.json file reflects the change with a new minor version as per [this](http://semver.org/), and I added myself as a contrib :)
- It's been tested against the example code that I added to the README.

If I polluted your README in ways you don't like, I'm happy to remove it.  I just wanted to do comprehensive work first, and pare down later if necessary.