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)
s/response/payload/? to avoid the confusion between `res` and `response`?