Fix "new sentence, new line" warnings throughout so that formatters
can produce correct spacing between sentences.
join.1
Remove unnecessary Ns macros. These are not necessary for delimeters,
which get special treatment.
xinstall.1
Fix date in manual. The contents were last modified on 2016-12-03,
so use that instead of the invalid date.
grep.1
Fix escape sequence for `\<` and `\>`.
ed.1
Remove spurious `\\n` escape for the null-command.
Laslo: Fix some things pointed out by mandoc -Tlint:
1) replace empty lines with .Pp, we want to start a new
paragraph
2) Add a comma before the second item in SEE ALSO
3) Place SEE ALSO before STANDARDS, as is the convention
4) Update the man-date
