added setter to Iterable- and InitialElementProducer

can't be modified to always run perfectly

enhanced the docs for the benchmark so it can be used as example or for
demonstration

test still not working 100%

added list of words and their number of occurrence

set to the CompositeStage's thread;
first scaling test prototype

prototype works correctly, still no scaling

renamed DistributedMapCounter to MappingCounter;
added first draft of WordCounter

consumption);
added CountingMapMerger, see JavaDoc

removed unused code in UnboundedSpScPipe