The serverStatus command allows storage engines to append custom statistics to the output via the ServerStatusSection interface. We can use this to report additional Biggie metrics such as:

1. Reporting to the total memory usage of the radix trees still available in the history. We'll have to watch out to avoid double counting shared nodes between the trees. Today, Biggie only tracks the size of the stored values in data nodes only.
2. The average number of child nodes that each parent has. With the adaptive node work, this should decrease from 256 dramatically.