ps.1: Revamp: Explain general principles, update to match reality
The preamble has been revamped to give a thorough overview of the
different aspects of the ps(1) command in the following separate
paragraphs:
- What it outputs.
- Which processes are listed.
- Which information is displayed by process.
- How lines are sorted.
- Considerations about the (mostly broken) output width.
- Backwards compatibility features.
Fix or expand the description of several options and some keywords to
match their actual behavior.
Expand the STANDARDS section, noting the options conforming to POSIX and
those that do not (but may be changed to), as well as current diverging
behaviors.
Expand the BUGS section with a thorough description of other known
problems.
While here, document the POSIX-specified '-A' option. We have been
supporting it since 2004 (commit "Support more POSIX/SUSv3 options:",
a4c8a745a85b18d7, r127499) and it has been standard for longer. It
seems now highly unlikely we will ever want to use it for any other
purpose, so just stop trying to hide it.
While here, re-order flags according to mdoc(7)'s prescription. Given
the current state, this also requires less changes than, e.g., putting
all uppercase flags first.
While here, move the detailed specifications of keywords from the
DESCRIPTION to the KEYWORDS section.
While here, fix the formatting of some references to keywords.
MFC after: 3 days
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D49605