man4: use .Mt for emails (2/2)

This concludes the efforts to consistently use .Mt for
email addresses.  It also sneaks in a couple of subtle
changes to punctuation, grammar and conversion of
'.Nm xxx' to '.Xr xxx 4' where appropriate.
kernel: Remove some unused kmalloc types in drm/drm2 code.

OK'd: ftigeot
adjust grammar in a few man pages: s/was/were/
resolve mandoc(1) warnings in games/

larn.6 was redesigned in parts for readability.
sail.6 needs a separate commit.
unquote section names in man pages

While there, make them upper case, try to simplify and
consolidate, zap comments that nobody will ever see again
and tweak one AUTHORS instance with '.An -nosplit'.
dhclient.conf.5: .Nm needs a parameter only once.
sys/boot: Remove some unused externs.
sail.6: mdoc conversion

Synced from parts of both OpenBSD and NetBSD, with a little
tweaking in the AUTHORS section.  mandoc(1) warnings are gone.
sed.1/sail.6: Fix section references and a function name.
hexdump(1): clean up tables in man pages, output is lower-case
window.1: unbreak macros, hyphens are `-' not minus `\-'
Document isgreater(3) and friends.
<sys/proc.h>: Remove suser() and suser_cred() prototypes.

suser_*() was replaced with priv_*() more than 4 years ago.

Reported-by: Joris Giovannangeli <joris@giovannangeli.fr>
taskqueue.9: Use .Er for errors numbers.
kernel: Stop installing pst(4) module and manual page on x86_64.

It is i386 only.
Fix typo in MLINKS line for taskqueue_drain_timeout(9).
strchr.3: Fix typo, it's strchrnul, not strrchrnul.
libm: Fix a typo in the MLINKS line for log2l(3).
kether_ntoa.9: Small whitespace fix.
Remove 'device firmware' from various manpages because it is not optional.