Split off .rotor from .buffering

S17-concurrency.pod

@@ -601,16 +601,21 @@ L<List.squish>).
 
   my $b = $s.buffering( :elems(100), :seconds(1) );
 
-  my $b = $s.buffering( :elems(2), :overlap(1) );
-
 Produces a C<Supply> that buffers the values of the given Supply by either
 the number of elements (using the C<elems> named parameter) or the maximum
-number of seconds (using the C<seconds> named parameter) or both.
+number of seconds (using the C<seconds> named parameter) or both.  Values
+are grouped in a single array element when flushed.
+
+=item rotor
+
+  my $b = $s.rotor( $elems, $overlap );
 
-Or produces a "rotoring" C<Supply> where the last elements (as specified by
-the C<overlap> named parameter) are kept when the buffer is flushed.
+  my $b = $s.rotor;    # elems = 2, overlap = 1
 
-Values are grouped in a single array element when flushed.
+Produces a "rotoring" C<Supply> where every C<elems> number of elements are
+combined, and the last C<overlap> elements of such a combination become the
+initial elements of the next combination.  This can e.g. be used to convert
+a C<Supply> of coordinates into a C<Supply> of begin/end points.
 
 =item delayed