Create some interesting Map/Reduce style examples

As interesting as the reverse_* clients/workers are, we need better examples. We can look at other examples that Google or Hadoop use, such as:

http://hadoop.apache.org/core/docs/r0.15.2/api/org/apache/hadoop/examples/package-summary.html

We need to pick some of these and show how they can be implemented, and stick the code in the examples directory.