1) Improve the documentation of the SSL module, with a fuller
   explanation of certificate usage, another reference, proper
   formatting of this and that.

2) Fix Windows bug in ssl.py, and general bug in sslsocket.close().
   Remove some unused code from ssl.py.  Allow accept() to be called on
   sslsocket sockets.

3) Use try-except-else in import of ssl in socket.py.  Deprecate use of
   socket.ssl().

4) Remove use of socket.ssl() in every library module, except for
   test_socket_ssl.py and test_ssl.py.