Clarify the tests in embedded_test.go to indicate that unmarshalling
of an internal object (runtime.EmbeddedObject) will not work. Instead,
consumers should decode raw external objects.
* Make Codec separate from Scheme
* Move EncodeOrDie off Scheme to take a Codec
* Make Copy work without a Codec
* Create a "latest" package that imports all versions and
sets global defaults for "most recent encoding"
* v1beta1 is the current "latest", v1beta2 exists
* Kill DefaultCodec, replace it with "latest.Codec"
* This updates the client and etcd to store the latest known version
* EmbeddedObject is per schema and per package now
* Move runtime.DefaultScheme to api.Scheme
* Split out WatchEvent since it's not an API object today, treat it
like a special object in api
* Kill DefaultResourceVersioner, instead place it on "latest" (as the
package that understands all packages)
* Move objDiff to runtime.ObjectDiff
