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.
Merge branch 'master' into gsocdrm_alter