[$] Rationalizing Python's APIs

<p>CPython is the reference implementation of Python, so it is,unsurprisingly, the target for various language-extension modules. But theAPI and ABI it provides to those extensions ends up limiting whatalternative Python implementations-and even CPython itself-can do, sincethose interfaces must continue to be supported. Beyond that, though, theinterfaces are not clearly delineated, so changes can unexpectedly affect extensionsthat have come to depend on them. A recent thread on the python-ideasmailing list looks at how to clean that situation up.