add an example that runs wordcount over file datasets

simple example to read and write files. 
- a service that can upload/download files
- a mapreduce that reads/writes the same files, with runtime arguments to specify the paths

I am open to renaming this, if you have a better suggestion. 
This suggests we need a responder.sendErrorParameters method that saves having to write all these quotes...
like python's 
responder.sendErrorParameters( 400, "Unable to write path '%s' in file set '%s'" % ( filePath, set) )