Remove support for Python 2.7 on Windows (#68)

Mercurial 6.2 released in July 2022 removed support for Python 2.7.
It was the last project using pythoncapi_compat.h which required
Python 2.7 support (on Windows).

Remove PYCAPI_COMPAT_STATIC_INLINE() macro: use "static inline"
directly.

See:

* https://www.mercurial-scm.org/downloads
* https://wiki.mercurial-scm.org/SupportedPythonVersions

Author: vstinner

docs/api.rst

@@ -18,8 +18,7 @@ C++03 and C++11 are supported on Python 3.6 and newer.
 
 A C99 subset is required, like ``static inline`` functions: see `PEP 7
 <https://www.python.org/dev/peps/pep-0007/>`_.  ISO C90 is partially supported
-for Python 2.7 and Visual Studio 2008 (avoid mixed declarations and code, ``gcc
--Werror=declaration-after-statement``).
+for Python 2.7.
 
 Some functions related to frame objects and ``PyThreadState`` are not available
 on PyPy.

docs/changelog.rst

@@ -1,6 +1,7 @@
 Changelog
 =========
 
+* 2023-08-21: Remove support for Python 2.7, Python 3.4 and older.
 * 2023-08-16: Add ``Py_IsFinalizing()`` function.
 * 2023-07-21: Add ``PyDict_GetItemRef()`` function.
 * 2023-07-18: Add ``PyModule_Add()`` function.