!per #3652 Custom snapshot and persistent message serialization

- Protobuf serializer for Persistent message
- Configurable serializer for Persistent message's payload
- Configurable serializer for snapshots

akka-docs/rst/java/code/docs/persistence/PersistenceDocTest.java

@@ -1,3 +1,7 @@
+/**
+ * Copyright (C) 2009-2013 Typesafe Inc. <http://www.typesafe.com>
+ */
+
 package docs.persistence;
 
 import scala.Option;