Make use of kryo more configurable

- Move away from thread local in favour of using
  kryo pooling.
- New interface StateMachineSerialisationService
  with KryoStateMachineSerialisationService.
- Try to work via constructors for instead of full blown
  configuration as it looks like this may give enough
  for users to customise.
- Relates to #437

spring-statemachine-core/src/main/java/org/springframework/statemachine/service/StateMachineSerialisationService.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2017 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.statemachine.service;
+
+import org.springframework.statemachine.StateMachineContext;
+
+/**
+ * Generic interface to handle serialisation in a state machine.
+ *
+ * @author Janne Valkealahti
+ *
+ * @param <S> the type of state
+ * @param <E> the type of event
+ */
+public interface StateMachineSerialisationService<S, E> {
+
+	/**
+	 * Serialise state machine context into byte array.
+	 *
+	 * @param context the context
+	 * @return the data as byte[]
+	 * @throws Exception the exception when serialisation fails
+	 */
+	byte[] serialiseStateMachineContext(StateMachineContext<S, E> context) throws Exception;
+
+	/**
+	 * Deserialise state machine context from byte array.
+	 *
+	 * @param data the data
+	 * @return the state machine context
+	 * @throws Exception the exception when deserialisation fails
+	 */
+	StateMachineContext<S, E> deserialiseStateMachineContext(byte[] data) throws Exception;
+}