Make the err(3) manual clearer to read.

- Mention that the 'fmt' argument to these functions holds
a printf(3)-like format specification.
- Clarify that the err()/warn()/errc()/warnc() family of functions
will append an additional error message to the output.
- Add whitespace to separate paragraphs describing distinct
concepts.
- Move the sentence mentioning the final output newline to
a less ambiguous location within the text.
- Add a cross-reference to printf(3).

Add errc() and verrc() to the list of functions which do not return,
but exit() instead.

This was omitted when the *c() set of functions were added in 2014.

branches: 1.22.8; 1.22.16;
Remove workaround for ancient HTML generation code.

branches: 1.21.18;
Add the {v,}{err,warn}c flavors, from FreeBSD.

branches: 1.20.6; 1.20.12;
Use .In for header files instead of .Ar Pa and variations.

Be more explicit about the difference between the err and errx (and
similar) functions. Based on wording from Jeremy C. Reed.
Closes PR 22424.

Move UCB-licensed code from 4-clause to 3-clause licence.

Patches provided by Joel Baker in PR 22280, verified by myself.

Use
.In header.h
instead of
.Fd #include \*[Lt]header.h\*[Gt]
Much easier to read and write, and supported by groff for ages.
Okayed by ross.

\-1 and .Dv NULL.

import CAVEATS sections from OpenBSD.
with little tweak by me.

Generate <>& symbolically.

Boring whitespace fixes.

clean up a bit, xref exit(3), and suggest use of EXIT_FAILURE.

branches: 1.11.2;
add cross-reff to getprogname(3)

Last of the .Os cleanups. .Os is defined in the tmac.doc-common file,
so we shouldn't override it with versions in the manpages. Wheee!

add LIBRARY section to man page

Use warn() instead of err() as an example of ``Warn of an error''.

Fix broken uses of Dd. Both the mdoc and mdoc.samples pages agree:
.Dd is supposed to be invoked like:
.Dd month day, year
e.g. ".Dd January 25, 1989", rather than:
.Dd "month day, year"
which is what these pages did.

clarify what is printed; from Arne Henrik Juul in PR 3242, with some
minor editing by myself.

update to 4.4-Lite where appropriate, clean up Id format, etc.

Misc manpage fixes.

update to latest version; no *significant* changes.

Add RCS identifiers.

branches: 1.1.1;
new err stuff