GH-65: Add polled-consumer Sample

Resolves https://github.com/spring-cloud/spring-cloud-stream-samples/issues/65

Polishing - PR Comments

- add docker-compose
- change runner to process multiple messages

processor-samples/polled-consumer/README.md

@@ -0,0 +1,57 @@
+Spring Cloud Stream Polled Consumer with Embedded Kafka Broker Sample
+=====================================================================
+
+In this *Spring Cloud Stream* sample, an embedded kafka broker is used for testing a polled consumer.
+
+## Requirements
+
+To run this sample, you will need to have installed:
+
+* Java 8 or Above
+
+## Code Tour
+
+This sample is a Spring Boot application that uses Spring Cloud Stream to receive a `String` message and forward an upper case version of that String; it uses the Kafka binder.
+It uses a Polled Consumer (rather than a message-driven `@StreamListener`).
+
+* PolledConsumerApplication - the Spring Boot Main Application
+* PolledConsumerApplicationTests - the test case
+
+The `spring-kafka-test` dependency added to the `pom.xml` puts the `KafkaEmbedded` JUnit `@Rule` on the class path.
+Refer to the [Spring for Apache Kafka Reference Manual](http://docs.spring.io/spring-kafka/reference/htmlsingle/#testing) for more information about this.
+Notice how the `@BeforeClass` method sets up the Boot and binder properties to locate the servers.
+
+See the test method for the details on interacting with Embedded Kafka.
+The test method starts by sending a message to the input destination.
+It then creates a consumer to consume from the output destination; gets the output message and asserts that it's an upper case version of the sent message.
+
+## Building with Maven
+
+Build the sample and run the test by executing:
+
+`./mvnw clean package`
+
+or run the test in your favorite IDE.
+
+=== Running the app:
+
+Go to the root of the repository and do:
+
+`docker-compose up -d`
+
+`./mvnw clean package`
+
+`java -jar target/polled-consumer-0.0.1-SNAPSHOT.jar`
+
+Then send/receive messages to/from the topics.
+
+`$ docker exec -it kafka-polledconsumer /opt/kafka/bin/kafka-console-producer.sh --broker-list 127.0.0.1:9092 --topic polledConsumerIn`
+
+On another terminal:
+
+and
+
+`$ docker exec -it kafka-polledconsumer /opt/kafka/bin/kafka-console-consumer.sh --bootstrap-server 127.0.0.1:9092 --topic polledConsumerOut --from-beginning`
+
+Once you are done testing, stop the Kafka cluster: `docker-compose down`
+