1) Shorten synopsis and reflect this in the manual
2) Use argv0 in usage()
3) Decrement argc in argv-loop for consistency
4) Make it clearer which error-code results from which errno in enprintf
5) Use idiomatic for-loop also for environ. Don't increment these pointers
in the loop itself!
- add .Os, it is mandatory.
- don't redeclare .Nm when it's not needed.
- fix some warnings (checked with mandoc -Tlint).
- remove some leftover old stuff.
