Revert "Undocument .later plurals"

This reverts commit 9aa6832.

Author: lizmat

doc/Type/Date.pod

@@ -23,7 +23,7 @@ an object the current day according to the system clock.
     say $d.month;                   # 12
     say $d.day;                     # 24
     say $d.day-of-week;             # 1  (that's Monday)
-    say $d.later(day => 20);        # 2016-01-13
+    say $d.later(days => 20);       # 2016-01-13
     my $n = Date.new('2015-12-31'); # New Year's Eve
     say $n - $d;                    # 7 days between New Years/Christmas Eve
     say $n + 1;                     # 2016-01-01
@@ -81,21 +81,22 @@ Returns a Date object based on the current one, but with a date delta
 applied. The date delta can be passed as a named argument where the argument
 name is the unit.
 
-Allowed units are C<day>, C<week>, C<month>, C<year>.
+Allowed units are C<day>, C<days>, C<week>, C<weeks>, C<month>, C<months>,
+C<year>, C<years>.
 
 Please note that the special ":2nd" named parameter syntax can be a compact
 and self-documenting way of specifying the delta
 
-    say Date.new('2015-12-24').later(:2year);
+    say Date.new('2015-12-24').later(:2years);
         # 2017-12-24
 
 Since addition of several different time units is not commutative, only one
 unit may be passed.
 
     my $d = Date.new('2015-02-27');
-    say $d.later(month => 1).later(:2day);  # 2015-03-29
-    say $d.later(day => 2).later(:1month);  # 2015-04-01
-    say $d.later(day => 2).later(:month);   # same, as +True === 1
+    say $d.later(month => 1).later(:2days);  # 2015-03-29
+    say $d.later(days => 2).later(:1month);  # 2015-04-01
+    say $d.later(days => 2).later(:month);   # same, as +True === 1
 
 Negative offsets are allowed, though L<#method earlier> is more idiomatic for
 that.

doc/Type/DateTime.pod

@@ -29,7 +29,7 @@ my $dt = DateTime.new(
 );
 
 say $dt;                            # 2015-11-21T16:01:00Z
-say $dt.later(day => 20);           # 2015-12-11T16:01:00Z
+say $dt.later(days => 20);          # 2015-12-11T16:01:00Z
 say $dt.truncated-to('hour');       # 2015-11-21T16:00:00Z
 say $dt.in-timezone(-8 * 3600);     # 2015-11-21T08:01:00-0800
 
@@ -293,22 +293,23 @@ Returns a DateTime object based on the current one, but with a time delta
 applied. The time delta can be passed as a named argument where the argument
 name is the unit.
 
-Allowed units are C<second>, C<minute>, C<hour>, C<day>, C<week>, C<month>,
-C<year>.
+Allowed units are C<second>, C<seconds>, C<minute>, C<minutes>, C<hour>,
+C<hours>, C<day>, C<days>, C<week>, C<weeks>, C<month>, C<months>, C<year>,
+C<years>.
 
 Please note that the special ":2nd" named parameter syntax can be a compact
 and self-documenting way of specifying the delta
 
-    say DateTime.new('2015-12-24T12:23:00Z').later(:2year);
+    say DateTime.new('2015-12-24T12:23:00Z').later(:2years);
         # 2017-12-24T12:23:00Z
 
 Since addition of several different time units is not commutative, only one
 unit may be passed.
 
     my $d = DateTime.new(date => Date.new('2015-02-27'));
-    say $d.later(month => 1).later(:2day);  # 2015-03-29T00:00:00Z
-    say $d.later(day => 2).later(:1month);  # 2015-04-01T00:00:00Z
-    say $d.later(day => 2).later(:month);   # same, as +True === 1
+    say $d.later(month => 1).later(:2days);  # 2015-03-29T00:00:00Z
+    say $d.later(days => 2).later(:1month);  # 2015-04-01T00:00:00Z
+    say $d.later(days => 2).later(:month);   # same, as +True === 1
 
 Negative offsets are allowed, though L<#method earlier> is more idiomatic for
 that.