lib/sh/util.sh: logging: documented `make` equivalents of the various verbosities, where available. (many of the verbosities, such as level 1, are sorely needed in make to avoid excessive output.)

1. verbosities (and `make` equivalents):
2. 0: just print errors. useful for cron jobs.
3. vs. make: equivalent to --silent
4. 1: also external commands run. useful for running at the command line.
5. vs. make: not provided (but sorely needed to avoid excessive output)
6. 2: full graphical call tree. useful for determining where error occurred.
7. vs. make: equivalent to default verbosity, but with much-needed indents
8. 3: also values of kw params and variables. useful for low-level debugging.
9. vs. make: not provided; need to manually use $(error $(var))
10. 4: also variables in util.sh commands. useful for debugging util.sh.
11. vs. make: somewhat similar to --print-data-base
12. 5: also variables in logging commands themselves. useful for debugging echo_*.
13. vs. make: not provided; need to search Makefile for @ at beginning of cmd
14. 6+: not currently used (i.e. same as 5)