#22903 Fix code snippeds

* move scala and java sources out of paradox sources
* replace relative paths with $code$ and $akka$
* fix broken includes

akka-docs/src/main/scala/docs/dispatcher/MyUnboundedMailbox.scala

@@ -0,0 +1,60 @@
+/**
+ * Copyright (C) 2009-2017 Lightbend Inc. <http://www.lightbend.com>
+ */
+
+package docs.dispatcher
+
+//#mailbox-implementation-example
+import akka.actor.ActorRef
+import akka.actor.ActorSystem
+import akka.dispatch.Envelope
+import akka.dispatch.MailboxType
+import akka.dispatch.MessageQueue
+import akka.dispatch.ProducesMessageQueue
+import com.typesafe.config.Config
+import java.util.concurrent.ConcurrentLinkedQueue
+import scala.Option
+
+// Marker trait used for mailbox requirements mapping
+trait MyUnboundedMessageQueueSemantics
+
+object MyUnboundedMailbox {
+  // This is the MessageQueue implementation
+  class MyMessageQueue extends MessageQueue
+    with MyUnboundedMessageQueueSemantics {
+
+    private final val queue = new ConcurrentLinkedQueue[Envelope]()
+
+    // these should be implemented; queue used as example
+    def enqueue(receiver: ActorRef, handle: Envelope): Unit =
+      queue.offer(handle)
+    def dequeue(): Envelope = queue.poll()
+    def numberOfMessages: Int = queue.size
+    def hasMessages: Boolean = !queue.isEmpty
+    def cleanUp(owner: ActorRef, deadLetters: MessageQueue) {
+      while (hasMessages) {
+        deadLetters.enqueue(owner, dequeue())
+      }
+    }
+  }
+}
+
+// This is the Mailbox implementation
+class MyUnboundedMailbox extends MailboxType
+  with ProducesMessageQueue[MyUnboundedMailbox.MyMessageQueue] {
+
+  import MyUnboundedMailbox._
+
+  // This constructor signature must exist, it will be called by Akka
+  def this(settings: ActorSystem.Settings, config: Config) = {
+    // put your initialization code here
+    this()
+  }
+
+  // The create method is called to create the MessageQueue
+  final override def create(
+    owner:  Option[ActorRef],
+    system: Option[ActorSystem]): MessageQueue =
+    new MyMessageQueue()
+}
+//#mailbox-implementation-example