modularizing server and introduce cli example.

Following up from https://github.com/GoogleCloudPlatform/google-cloud-datastore/pull/50, this sent the server files to a new `/server` directory, as well as introduced a CLI example a little more sophisticated than the one from the earlier PR.

An easier to look at representation: https://github.com/stephenplusplus/gcloud-node-todos

![screen shot 2014-09-26 at 3 13 33 pm](https://cloud.githubusercontent.com/assets/723048/4426388/08dfd2ca-45b3-11e4-9f7b-b95a6b08d8e1.png)
It's one of those situations where you pick it and just be consistent in your own code. The only benefit to one over another is readability, but as these are all common ways of writing JavaScript, they should each offer the same readability to a newcomer.

If you prefer to look at:
```js
module.exports.getAll = function() {
  // ...
};
```

I'm happy to go that route :+1: