Link set and frozenset function docs to their class definitions (issue #16436).

Doc/library/functions.rst

@@ -541,11 +541,13 @@ are always available.  They are listed here in alphabetical order.
 .. function:: frozenset([iterable])
    :noindex:
 
-   Return a frozenset object, optionally with elements taken from *iterable*.
-   The frozenset type is described in :ref:`types-set`.
+   Return a new :class:`frozenset` object, optionally with elements taken from
+   *iterable*.  ``frozenset`` is a built-in class.  See :class:`frozenset` and
+   :ref:`types-set` for documentation about this class.
 
-   For other containers see the built in :class:`dict`, :class:`list`, and
-   :class:`tuple` classes, and the :mod:`collections` module.
+   For other containers see the built-in :class:`set`, :class:`list`,
+   :class:`tuple`, and :class:`dict` classes, as well as the :mod:`collections`
+   module.
 
 
 .. function:: getattr(object, name[, default])
@@ -1167,8 +1169,13 @@ are always available.  They are listed here in alphabetical order.
 .. function:: set([iterable])
    :noindex:
 
-   Return a new set, optionally with elements taken from *iterable*.
-   The set type is described in :ref:`types-set`.
+   Return a new :class:`set` object, optionally with elements taken from
+   *iterable*.  ``set`` is a built-in class.  See :class:`set` and
+   :ref:`types-set` for documentation about this class.
+
+   For other containers see the built-in :class:`frozenset`, :class:`list`,
+   :class:`tuple`, and :class:`dict` classes, as well as the :mod:`collections`
+   module.
 
 
 .. function:: setattr(object, name, value)