Moving Kite Dataset API info from old guide per CDK-753.

Link to the old guide from which this came. This is just shards of information brought forward so they're not lost. This info should be woven into the samples before 1.0.

http://kitesdk.org/docs/current/kite-data/guide.html
This can be combined with the next paragraph by inserting the definition of object model: "Kite uses Avro's object models, which are in-memory representations of data. Applications can be written to use the same object classes and any of the supported data formats. Changing the underlying storage format is as simple as switching the dataset URI"

Note "dataset's URI" changes to "dataset URI". Because URI identifies the dataset, you can't change a dataset's URI.