bpo-40066: Enum: modify `repr()` and `str()` (GH-22392)

* Enum: streamline repr() and str(); improve docs

- repr() is now ``enum_class.member_name``
- stdlib global enums are ``module_name.member_name``
- str() is now ``member_name``
- add HOW-TO section for ``Enum``
- change main documentation to be an API reference
diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index fa77406..4ef1fb8 100644
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -381,7 +381,7 @@ def test_str_for_enums(self):
         # Make sure that the PROTOCOL_* constants have enum-like string
         # reprs.
         proto = ssl.PROTOCOL_TLS
-        self.assertEqual(str(proto), '_SSLMethod.PROTOCOL_TLS')
+        self.assertEqual(str(proto), 'PROTOCOL_TLS')
         ctx = ssl.SSLContext(proto)
         self.assertIs(ctx.protocol, proto)