Update to current version of the MapReduce API

[thiloplanz]

It seems that a lot of things have changed in the MapReduce API, so these examples do not work anymore, at least not out-of-the-box. It is not immediately clear if only simple refactorings have to be done, or if there are bigger modifications necessary.

Please update the code to match the current API.

[mufumbo]

This would be great. I'm trying hard to find documentation on how to migrate this to the new pattern. Nothing found.

At least add a big message at the README.md, before people waste time.