Correct docs for ABCs (MutableSequence was missing __setiem). Simplify the...

Correct docs for ABCs (MutableSequence was missing __setiem).  Simplify the table by taking out inherited requirements for abstract methods.

Doc/library/collections.rst

@@ -57,31 +57,29 @@ ABC                        Inherits               Abstract Methods        Mixin
 :class:`Callable`                                 ``__call__``
 
 :class:`Sequence`          :class:`Sized`,        ``__getitem__``         ``__contains__``. ``__iter__``, ``__reversed__``.
-                           :class:`Iterable`,     and ``__len__``         ``index``, and ``count``
+                           :class:`Iterable`,                             ``index``, and ``count``
                            :class:`Container`
 
-:class:`MutableSequence`   :class:`Sequence`      ``__getitem__``         Inherited Sequence methods and
+:class:`MutableSequence`   :class:`Sequence`      ``__setitem__``         Inherited Sequence methods and
                                                   ``__delitem__``,        ``append``, ``reverse``, ``extend``, ``pop``,
-                                                  ``insert``,             ``remove``, and ``__iadd__``
-                                                  and ``__len__``
+                                                  and ``insert``          ``remove``, and ``__iadd__``
 
-:class:`Set`               :class:`Sized`,        ``__len__``,            ``__le__``, ``__lt__``, ``__eq__``, ``__ne__``,
-                           :class:`Iterable`,     ``__iter__``, and       ``__gt__``, ``__ge__``, ``__and__``, ``__or__``
-                           :class:`Container`     ``__contains__``        ``__sub__``, ``__xor__``, and ``isdisjoint``
+:class:`Set`               :class:`Sized`,                                ``__le__``, ``__lt__``, ``__eq__``, ``__ne__``,
+                           :class:`Iterable`,                             ``__gt__``, ``__ge__``, ``__and__``, ``__or__``
+                           :class:`Container`                             ``__sub__``, ``__xor__``, and ``isdisjoint``
 
 :class:`MutableSet`        :class:`Set`           ``add`` and             Inherited Set methods and
                                                   ``discard``             ``clear``, ``pop``, ``remove``, ``__ior__``,
                                                                           ``__iand__``, ``__ixor__``, and ``__isub__``
 
-:class:`Mapping`           :class:`Sized`,        ``__getitem__``,        ``__contains__``, ``keys``, ``items``, ``values``,
-                           :class:`Iterable`,     ``__len__``. and        ``get``, ``__eq__``, and ``__ne__``
-                           :class:`Container`     ``__iter__``
+:class:`Mapping`           :class:`Sized`,        ``__getitem__``         ``__contains__``, ``keys``, ``items``, ``values``,
+                           :class:`Iterable`,                             ``get``, ``__eq__``, and ``__ne__``
+                           :class:`Container`
+
+:class:`MutableMapping`    :class:`Mapping`       ``__setitem__`` and     Inherited Mapping methods and
+                                                  ``__delitem__``         ``pop``, ``popitem``, ``clear``, ``update``,
+                                                                          and ``setdefault``
 
-:class:`MutableMapping`    :class:`Mapping`       ``__getitem__``         Inherited Mapping methods and
-                                                  ``__setitem__``,        ``pop``, ``popitem``, ``clear``, ``update``,
-                                                  ``__delitem__``,        and ``setdefault``
-                                                  ``__iter__``, and
-                                                  ``__len__``
 
 :class:`MappingView`       :class:`Sized`                                 ``__len__``
 :class:`KeysView`          :class:`MappingView`,                          ``__contains__``,