[issue35134] Add a new Include/unstable/ subdirectory for the "unstable" API

[STINNER Victor]

Change by STINNER Victor <vstinner at redhat.com>:


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title: Move !Py_LIMITED_API to Include/pycapi/ -> Add a new Include/unstable/ subdirectory for the "unstable" API

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35134>
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