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)
This makes sense for the CLI. Where it's currently making a request to `GET /todos` for example, I can have it use a global `datastore.getTodos()`, and follow suit for the other methods.

I imagine we will have something like `$ gulp serve` that will start the API server as well as serve the web files: api = localhost:8080/todos, examples = localhost:8080/examples/web/angular/index.html. The web examples will use their conventional xhr methods to ping the API server directly. I don't see how we can use the proposed module for the web apps, but that could just be me not catching on to something that should be obvious :confused: It wouldn't be the first time!