lib/sh/util.sh: logging: added description of the verbosities available, including what each one does and what it's useful for:

1. verbosities:
2. 0: just print errors. useful for cron jobs.
3. 1: also external commands run. useful for running at the command line.
4. 2: full graphical call tree. useful for determining where error occurred.
5. 3: also values of variables. useful for low-level debugging.
6. 4: also variables in util.sh commands. useful for debugging util.sh.
7. 5: also variables in logging commands themselves. useful for debugging echo_*.
8. 6+: not currently used (i.e. same as 5)