PEP 489: Multi-phase extension module initialization

Known limitations of the current implementation:

- documentation changes are incomplete
- there's a reference leak I haven't tracked down yet

The leak is most visible by running:

  ./python -m test -R3:3 test_importlib

However, you can also see it by running:

  ./python -X showrefcount

Importing the array or _testmultiphase modules, and
then deleting them from both sys.modules and the local
namespace shows significant increases in the total
number of active references each cycle. By contrast,
with _testcapi (which continues to use single-phase
initialisation) the global refcounts stabilise after
a couple of cycles.
diff --git a/Misc/ACKS b/Misc/ACKS
index 76f2df8..8a007ea 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1458,6 +1458,7 @@
 Jaap Vermeulen
 Nikita Vetoshkin
 Al Vezza
+Petr Victorin
 Jacques A. Vidrine
 John Viega
 Dino Viehland
diff --git a/Misc/NEWS b/Misc/NEWS
index 9239cbb..88ca513 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,8 @@
 Core and Builtins
 -----------------
 
+- Issue #24268: PEP 489: Multi-phase extension module initialization
+
 - Issue #23955: Add pyvenv.cfg option to suppress registry/environment
   lookup for generating sys.path on Windows.