sleep.1: miscellaneous rewrites, cleanup

sleep.1: miscellaneous rewrites, cleanup

Description

- "for a minimum of" is better said "for at least".

- The seconds argument can be zero, so say "non-negative".

- Specify that the number (the whole thing) is decimal to exclude
  e.g. hex numbers.  It then follows that the optional fraction
  must also be decimal.

- No need to inspire the reader to use sleep(1) in any particular way.
  It is probably sufficient to demonstrate these patterns in the Examples
  section later.

Asynchronous Events

- Note that SIGALRM wakes sleep(1) up "early".

Examples

- Simplify the first example.  Parenthetically pointing the reader to
  at(1) muddies what is otherwise a trivial example.  We can still point
  the reader to at(1) in the See Also section later.

- Shorten the interval in the first example.  A half hour is not
  interactive.

- Get rid of the entire csh(1) example.  It's extremely complex and
  the bulk of the text is spent explaining things that aren't about
  sleep(1) at all.

- Tweak the third example to show the reader that you can sleep
  for a fraction of a second, as mentioned in the Description.

Standards

- Prefer active voice.

  "The handling of fractional arguments" is better said
  "Support for fractional seconds".

  Shorten "is provided as" to "is".

History

- Not merely "appeared": "first appeared".

- Note that sleep(1) was reimplemented for 4.4BSD.

Thread: https://marc.info/?l=openbsd-tech&m=165888826603953&w=2

Lots of nice tweaks from jmc@.  Typo spotted by Crystal Kolipe.

ok jmc@