Resetting the flag should only occur in Enable() and Reset().
IterativeRobotBase needs the flag to remain set to print epochs after
disabling the Watchdog.
Notifier has one thread per instance because the callbacks must be
asynchronous. Watchdog callbacks can be synchronous, so this overhead
can be done away with via a scheduler thread akin to what the HAL
Notifier does.
The old headers were moved into folders because doing so avoids polluting
the system include directories.
Folder names were also normalized to lowercase.
