added setter to Iterable- and InitialElementProducer

Benchmark

Contains:

* the benchmark, as discussed
* a test for the benchmark (without testing data loss)
* a protected static method in CompositeStage, to connect stages
* final declaration of all classes
* signal-bug fix in Merger
* new images in the download page
* EveryXthPrinter extends CompositeStage
* moved util.test

See merge request !28

Conflicts:
	src/main/java/teetime/framework/RunnableConsumerStage.java
	src/site/markdown/wiki

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