man: use https URLs for www.NetBSD.org

branches: 1.10.2;
kern: Make time_second and time_uptime macros that work atomically.

These use atomic load on platforms with atomic 64-bit load, and
seqlocks on platforms without.

This has the unfortunate side effect of slightly reducing the real
times available on 32-bit platforms, from ending some time in the
year 584942417218 AD, available on 64-bit platforms, to ending some
time in the year 584942417355 AD. But during that slightly shorter
time, 32-bit platforms can avoid bugs arising from non-atomic access
to time_uptime and time_second.

Note: All platforms still have non-atomic access problems for
bintime, binuptime, nanotime, nanouptime, &c. This can be addressed
by putting a seqlock around timebasebin and possibly some other
variable -- to be done in a later change.

XXX kernel ABI change -- deleting symbols

Remove trailing comma.

remove documentation for (non-atomic) boottime, it was eliminated
from kernel in 2020-01-02 by thorpej@

Minor update. This already knew that boottime is a timespec.
Just a minor wording change to avoid pretending that time_t
variables contain nanoseconds, and that the base time is UTC.

branches: 1.6.10; 1.6.12;
boottime is a timespec these days.
From Tomoyuki Sahara in PR 52059.

branches: 1.5.26; 1.5.30;
Tidy up the SEE ALSO section. Namely, do not duplicate a big list of xrefs
that are already used in the body of the text.

Use .Vt for variables, not .Va and manual line breaking.

branches: 1.3.2;
Fix typo, remove .Pp before .Sh (unneeded).

- reorder description per meanings
- note header files in SYNOPSIS
- remove obsolete internal description about hardclock(9)
- note that microtime(9) and microuptime(9) family functions are prefered
for atomic operation (from FreeBSD's time(9))
- add more related Xrefs

branches: 1.1.24;
time.9 renamed to time_second.9. various updates to reflect API changes.