Tune samples and update ref docs

- Fix cplayer play logic depending if we pressed
  eject or play.
- Updates to ref docs.

spring-statemachine-samples/cdplayer/src/main/java/demo/cdplayer/Application.java

@@ -196,6 +196,7 @@ public class Application  {
 		@Override
 		public void execute(StateContext<States, Events> context) {
 			if (context.getTransition() != null
+					&& context.getEvent() == Events.PLAY
 					&& context.getTransition().getTarget().getId() == States.CLOSED
 					&& context.getExtendedState().getVariables().get(Variables.CD) != null) {
 				context.getStateMachine().sendEvent(Events.PLAY);

spring-statemachine-samples/cdplayer/src/main/java/demo/cdplayer/CdPlayer.java

@@ -91,7 +91,7 @@ public class CdPlayer {
 	}
 
 //tag::snippetB[]
-	@StatesOnTransition(target = States.CLOSED)
+	@StatesOnTransition(target = {States.CLOSED, States.IDLE})
 	public void closed(ExtendedState extendedState) {
 		Object cd = extendedState.getVariables().get(Variables.CD);
 		if (cd != null) {