Expose extended state

- ExtendedState is now exposed via
  StateMachine interface.
- Add "sm variables" command to samples.

spring-statemachine-core/src/main/java/org/springframework/statemachine/StateMachine.java

@@ -37,6 +37,13 @@ public interface StateMachine<S, E> extends Region<S, E> {
 	 */
 	State<S,E> getInitialState();
 
+	/**
+	 * Gets the state machine extended state.
+	 *
+	 * @return extended state
+	 */
+	ExtendedState getExtendedState();
+
 	/**
 	 * Adds the state listener.
 	 *

spring-statemachine-core/src/main/java/org/springframework/statemachine/support/AbstractStateMachine.java

@@ -177,6 +177,11 @@ public abstract class AbstractStateMachine<S, E> extends LifecycleObjectSupport
 		return initialState;
 	}
 
+	@Override
+	public ExtendedState getExtendedState() {
+		return extendedState;
+	}
+
 	@Override
 	public boolean sendEvent(Message<E> event) {
 		if (isComplete() || !isRunning()) {