Relax the subject limit from 70 to 80 characters and the body
wrap limit from 76 to 80. Merge/Revert/Reapply commits skip the
subject length check since git prepends those prefixes to an
existing subject. Update the checker, its tests, and all related
docs and memories accordingly.
AI-assisted-by: muse-spark-1.3-contributor
Signed-off-by: Andrey Antukh <niwi@niwi.nz>