1) Clarify behaviour when the f-flag is given and a target is in its
own way.
2) Fix usage()-style.
3) Group local variable declarations.
4) reorder args
5) argc style, other boolean style changes
6) improve error messages
7) set argv[argc - 1] to NULL to allow argv-centric loop later
8) BUGFIX: POSIX specifies that when with the f-flag there's a
situation where a file stands in its own way for linking it
should be ignored.
9) Add weprintf() where possible, so we don't pussy out when there's
a small issue. This is sbase ffs!
- 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.
