Allow the stats to be overridden (for debugging)
More meaningful error when no URL specified.
Much better application design.

Stats are becoming more self-contained. One more step remaining.
All stats are now self-contained classes.
Config object replaced by namedtuple.

This further simplifies the code!
Auto-generation of command-map, docs.

The command map is now generated based on the subclass names of
FritzStat. No manual mapping is needed anymore.