Make runtime less global for Codec

* 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

pkg/runtime/interfaces.go

@@ -16,13 +16,23 @@ limitations under the License.
 
 package runtime
 
-// Codec defines methods for serializing and deserializing API objects.
-type Codec interface {
-	Encode(obj Object) (data []byte, err error)
+// Decoder defines methods for deserializing API objects into a given type
+type Decoder interface {
 	Decode(data []byte) (Object, error)
 	DecodeInto(data []byte, obj Object) error
 }
 
+// Encoder defines methods for serializing API objects into bytes
+type Encoder interface {
+	Encode(obj Object) (data []byte, err error)
+}
+
+// Codec defines methods for serializing and deserializing API objects.
+type Codec interface {
+	Decoder
+	Encoder
+}
+
 // ResourceVersioner provides methods for setting and retrieving
 // the resource version from an API object.
 type ResourceVersioner interface {