Fix various lint warnings in manuals

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.

grep.1

@@ -17,7 +17,8 @@ searches the input files for lines that match the
 .Ar pattern ,
 a regular expression as defined in
 .Xr regex 7 .
-By default each matching line is printed to stdout. If no
+By default each matching line is printed to stdout.
+If no
 .Ar file
 is given
 .Nm
@@ -27,11 +28,12 @@ reads from stdin.
 .It Fl E
 Match using extended regex.
 .It Fl F
-Match using fixed strings. Treat each pattern specified as a string instead of
-a regular expression.
+Match using fixed strings.
+Treat each pattern specified as a string instead of a regular
+expression.
 .It Fl H
-Prefix each matching line with its filename in the output. This is the
-default when there is more than one file specified.
+Prefix each matching line with its filename in the output.
+This is the default when there is more than one file specified.
 .It Fl c
 Print only a count of matching lines.
 .It Fl e Ar pattern
@@ -41,9 +43,10 @@ This option is most useful when multiple -e options are used to
 specify multiple patterns, or when a pattern begins with a dash.
 .It Fl f Ar file
 Read one or more patterns from the file named by the pathname file.
-Patterns in file shall be terminated by a <newline>. A null pattern can be
-specified by an empty line in pattern_file. Unless the -E or -F option is
-also specified, each pattern shall be treated as a BRE.
+Patterns in file shall be terminated by a <newline>.
+A null pattern can be specified by an empty line in pattern_file.
+Unless the -E or -F option is also specified, each pattern shall be
+treated as a BRE.
 (`-').
 .It Fl h
 Do not prefix each line with 'filename:' prefix.
@@ -63,7 +66,7 @@ Select lines which do
 .Sy not
 match the pattern.
 .It Fl w
-The expression is searched for as a word (as if surrounded by '\<' and '\>').
+The expression is searched for as a word (as if surrounded by '\\<' and '\\>').
 .It Fl x
 Consider only input lines that use all characters in the line excluding the
 terminating <newline> to match an entire fixed string or regular expression to