Clarify that gevent.pywsgi is the replacement for gevent.wsgi. [skip ci]

Also fix the formatting in changelog_1_0.rst so it renders legibly.

doc/api/gevent.wsgi.rst

+==========================================================
+ ``gevent.wsgi`` -- Historical note only; does not exist
+==========================================================
+
+.. warning::
+
+   Beginning in gevent 1.3, this module no longer exists.
+
+Starting in gevent 1.0a1 (2011), this module was nothing more than
+an alias for :mod:`gevent.pywsgi`, which is what should be used instead.
+
+Prior to gevent 1.0, when gevent was based on libevent,
+``gevent.wsgi`` used libevent's http support, but that was dropped
+with the introduction of libev. libevent's http support had several
+limitations, including not supporting stream, not supporting
+pipelining, and not supporting SSL.

doc/api/index.rst

@@ -86,6 +86,7 @@ Deprecated Modules
 .. toctree::
 
    gevent.ares
+   gevent.wsgi
 
 Examples
 ========

doc/whatsnew_1_3.rst

@@ -168,15 +168,21 @@ Compatibility
 This release is intended to be compatible with 1.2.x with no changes
 to client source code, so long as only non-deprecated and supported
 interfaces were used (as always, internal, non-documented
-implementation details may have changed).
-
-The :doc:`resolvers <dns>` have been refactored. As a result,
-``gevent.ares``, ``gevent.resolver_ares`` and
-``gevent.resolver_thread`` have been deprecated. Choosing a resolver
-by alias (e.g., 'thread') in the ``GEVENT_RESOLVER`` environment
-variable continues to work as before.
-
-The internal module ``gevent._threading`` was significantly
-refactored. The long-deprecated module ``gevent.wsgi`` was removed.
+implementation details may have changed). Here are some specific
+compatibility notes.
+
+- The :doc:`resolvers <dns>` have been refactored. As a result,
+  ``gevent.ares``, ``gevent.resolver_ares`` and
+  ``gevent.resolver_thread`` have been deprecated. Choosing a resolver
+  by alias (e.g., 'thread') in the ``GEVENT_RESOLVER`` environment
+  variable continues to work as before.
+
+- The internal module ``gevent._threading`` was significantly
+  refactored. As the name indicates this is an internal module not
+  intended as part of the public API, but such uses have been observed.
+
+- The module ``gevent.wsgi`` was removed. Use :mod:`gevent.pywsgi`
+  instead. ``gevent.wsgi`` was nothing but an alias for
+  :mod:`gevent.pywsgi` since gevent 1.0a1 (2011).
 
 ..  LocalWords:  Greenlet