Add script to run examples

Apache Spark has a convenience script ./bin/run-example to allow users to quickly run the pre-packaged examples without having to compose a long(ish) spark-submit command. The JavaDoc of most examples refers to that ./bin/run-example script in their description of how to run that example.

The Apache Bahir project should have a similar convenience script to be consistent with Apache Spark, existing documentation and to (at least initially) hide additional complexities of the spark-submit command.

Example:

./bin/run-example \
  org.apache.spark.examples.streaming.akka.ActorWordCount localhost 9999

...translates to this spark-submit command:

${SPARK_HOME}/bin/spark-submit \
  --packages org.apache.bahir:spark-streaming-akka_2.11:2.0.0-SNAPSHOT \
  --class org.apache.spark.examples.streaming.akka.ActorWordCount \
    streaming-akka/target/spark-streaming-akka_2.11-2.0.0-SNAPSHOT-tests.jar \
  localhost 9999