added copyright header

fixed termination bug in RunnableConsumerStage;
added check in StageTester;
removed isStarted() in AbstractStage

AbstractProducer/ConsumerStage)

fixed Javadoc

declared all methods in CompositeStage final

Added some methods to the stage tester; Modified the distributor test in order to use the new stage tester

Stagetester

This merge would add a first version of my StageTester, allowing to test single stages within JUnit test cases.

See merge request !29

Distributor clone strategy

This merge would add an experimental implementation for the clone strategy of the distributor. It tries to create a new instance of incoming elements and uses available getters/setters to copy the values. Technically it is not a deep copy and I doubt it to be very fast. The additional JUnit test documents the functionality.

See merge request !30

added RunnableConsumerStageTest