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.

join.1

@@ -19,8 +19,8 @@ lines from
 .Ar file1
 and
 .Ar file2
-on a matching field. If one of the input files is '-', standard input
-is read for that file.
+on a matching field.
+If one of the input files is '-', standard input is read for that file.
 .Pp
 Files are read sequentially and are assumed to be sorted on the join
 field.
@@ -31,9 +31,9 @@ produce unexpected output.
 By default, input lines are matched on the first blank-separated
 field; output lines are space-separated and consist of the join field
 followed by the remaining fields from
-.Ar file1 Ns ,
+.Ar file1 ,
 then the remaining fields from
-.Ar file2 Ns .
+.Ar file2 .
 .Sh OPTIONS
 .Bl -tag -width Ds
 .It Fl 1 Ar field
@@ -50,12 +50,12 @@ Print unpairable lines from file
 in addition to normal output.
 .It Fl e Ar string
 When used with
-.Fl o Ns ,
+.Fl o ,
 replace empty fields in the output list with
-.Ar string Ns .
+.Ar string .
 .It Fl o Ar list
 Format output according to the string
-.Ar list Ns .
+.Ar list .
 Each element of
 .Ar list
 may be either
@@ -63,22 +63,24 @@ may be either
 or 0 (representing the join field).
 Elements in
 .Ar list
-may be separated by blanks or commas. For example,
+may be separated by blanks or commas.
+For example,
 .Bd -literal -offset indent
 join -o "0 2.1 1.3"
 .Ed
 .Pp
 would print the join field, the first field of
-.Ar file2 Ns ,
+.Ar file2 ,
 then the third field of
-.Ar file1 Ns .
+.Ar file1 .
 .Pp
 Only paired lines are formatted with the
 .Fl o
-option. Unpairable lines (selected with
+option.
+Unpairable lines (selected with
 .Fl a
 or
-.Fl v Ns )
+.Fl v )
 are printed raw.
 .It Fl t Ar delim
 Use the arbitrary string
@@ -98,7 +100,7 @@ specification with the following exeption:
 .Bl -bullet -offset indent
 .It
 Unpairable lines ignore formatting specified with
-.Fl o Ns .
+.Fl o .
 .El
 .Pp
 The possibility of specifying multibyte delimiters of arbitrary