Allow the state of the monitor to be saved and reloaded

[Sean Kauffman]

This is a major feature which would allow nfer to be used in much more practical, long running applications. The idea would be to add a flag that caused the state of all the caches to be saved on exit, and to allow loading the cache state from a saved file. This should mostly involve adding save/load functions to pool.

This might require that certain precautions are taken to avoid the caches growing without bound. That is a separate issue, though.