bpo-11233: Create availability directive for documentation (GH-9692)

Replace "Availability: xxx" with ".. availability:: xxx" in the doc.
Original patch by Georg Brandl.

Co-Authored-By: Georg Brandl <georg@python.org>
diff --git a/Doc/c-api/exceptions.rst b/Doc/c-api/exceptions.rst
index 2bc1bd8..dd1e026 100644
--- a/Doc/c-api/exceptions.rst
+++ b/Doc/c-api/exceptions.rst
@@ -186,34 +186,42 @@
    then it constructs a tuple object whose first item is the *ierr* value and whose
    second item is the corresponding error message (gotten from
    :c:func:`FormatMessage`), and then calls ``PyErr_SetObject(PyExc_WindowsError,
-   object)``. This function always returns *NULL*. Availability: Windows.
+   object)``. This function always returns *NULL*.
+
+   .. availability:: Windows.
 
 
 .. c:function:: PyObject* PyErr_SetExcFromWindowsErr(PyObject *type, int ierr)
 
    Similar to :c:func:`PyErr_SetFromWindowsErr`, with an additional parameter
-   specifying the exception type to be raised. Availability: Windows.
+   specifying the exception type to be raised.
+
+   .. availability:: Windows.
 
 
 .. c:function:: PyObject* PyErr_SetFromWindowsErrWithFilename(int ierr, const char *filename)
 
    Similar to :c:func:`PyErr_SetFromWindowsErrWithFilenameObject`, but the
    filename is given as a C string.  *filename* is decoded from the filesystem
-   encoding (:func:`os.fsdecode`).  Availability: Windows.
+   encoding (:func:`os.fsdecode`).
+
+   .. availability:: Windows.
 
 
 .. c:function:: PyObject* PyErr_SetExcFromWindowsErrWithFilenameObject(PyObject *type, int ierr, PyObject *filename)
 
    Similar to :c:func:`PyErr_SetFromWindowsErrWithFilenameObject`, with an
    additional parameter specifying the exception type to be raised.
-   Availability: Windows.
+
+   .. availability:: Windows.
 
 
 .. c:function:: PyObject* PyErr_SetExcFromWindowsErrWithFilenameObjects(PyObject *type, int ierr, PyObject *filename, PyObject *filename2)
 
    Similar to :c:func:`PyErr_SetExcFromWindowsErrWithFilenameObject`,
    but accepts a second filename object.
-   Availability: Windows.
+
+   .. availability:: Windows.
 
    .. versionadded:: 3.4
 
@@ -221,7 +229,9 @@
 .. c:function:: PyObject* PyErr_SetExcFromWindowsErrWithFilename(PyObject *type, int ierr, const char *filename)
 
    Similar to :c:func:`PyErr_SetFromWindowsErrWithFilename`, with an additional
-   parameter specifying the exception type to be raised. Availability: Windows.
+   parameter specifying the exception type to be raised.
+
+   .. availability:: Windows.
 
 
 .. c:function:: PyObject* PyErr_SetImportError(PyObject *msg, PyObject *name, PyObject *path)