Implement a statistics HTTP server

On my second pass, I still don't really understand how aggregation works.

This part is of key importance.  If you do this wrong, the numbers will be wrong.  

We really need a clear and concise text description of how aggregation works so we can make sure that it's the right algorithm and that the description in the text corresponds to the actual code.

Most of the other comments I've aren't about correctness and aren't as important as this.