Add tracing of option setting
nbtb <tool> -d you get an overview of all option settings (accumulated from config files and
the comand line).
It would be nice if that overview would show where the value was last set:
- from which config file it was read, or
- whether it came from the command line.
The latter may be harder to track, but could be the default.
Config file reading could add additional attributes to
to record the source of the value.
This will be helpful in understanding what is going on, and debugging option problems.