Added docs for Capture.antipairs

doc/Type/Capture.pod6

@@ -174,6 +174,25 @@ named arguments have their names as key.
     my Capture $c = \(2, 3, apples => (red => 2));
     say $c.pairs;                                     # (0 => 2 1 => 3 apples => red => 2)
 
+=head2 method antipairs
+
+Defined as:
+
+    multi method antipairs(Capture:D:) returns Seq:D
+
+Usage:
+
+    $capture.antipairs
+
+Returns all arguments, the positional followed by the named, as a
+L<Seq|/type/Seq> of L<pairs|/type/Pair> where the keys and values
+have been swapped, i.e. the value becomes the key and the key becomes
+the value. This behavior is the opposite of the L<pairs|#method_pairs>
+method.
+
+    my $capture = \(2, 3, apples => (red => 2));
+    say $capture.antipairs;                           # (2 => 0 3 => 1 (red => 2) => apples)
+
 =head2 method Bool
 
 Defined as: