Fix "new sentence, new line" warnings throughout so that formatters
can produce correct spacing between sentences.
Remove unnecessary Ns macros. These are not necessary for delimeters,
which get special treatment.
Fix date in manual. The contents were last modified on 2016-12-03,
so use that instead of the invalid date.
Fix escape sequence for `\<` and `\>`.
Remove spurious `\\n` escape for the null-command.
The one specified by mdoc is hard to read for non-native
speakers from countries which read the date day-first (like
Germany, Greece, North-Korea, Swamp,...).
This is also consistent with how we generally specify dates