bugfix: 'set' overloadable; further steps for multi threading support

doc/lib.txt

@@ -52,6 +52,8 @@ Collections and algorithms
 * `lists <lists.html>`_
   Nimrod linked list support. Contains singly and doubly linked lists and
   circular lists ("rings").
+* `queues <queues.html>`_
+  Implementation of a queue. The underlying implementation uses a ``seq``.
 * `intsets <intsets.html>`_
   Efficient implementation of a set of ints as a sparse bit set.