Global item mapping

Hi,

I added a feature that allows you to recursively rename multi-level arrays by defining a map of names.
This features works in addition to the "addMapping" Feature and has no BC breaks.

To test this feature and the current addMapping feature I also added a "TestWriter" Class. This was the only-thing that I could come up with that allowed me to test the output of a $workflow->process();

For further information I made a new README entry.