[3.8] bpo-38600: NULL -> ``NULL``. (GH-17001) (GH-17003)

Also fix some other formatting.
(cherry picked from commit e835b31d2b212c3c7820364398979cae2a9740b2)
diff --git a/Doc/c-api/number.rst b/Doc/c-api/number.rst
index 55ddb9c..620204c 100644
--- a/Doc/c-api/number.rst
+++ b/Doc/c-api/number.rst
@@ -275,8 +275,8 @@
    convert to a Py_ssize_t value would raise an :exc:`OverflowError`, then the
    *exc* argument is the type of exception that will be raised (usually
    :exc:`IndexError` or :exc:`OverflowError`).  If *exc* is ``NULL``, then the
-   exception is cleared and the value is clipped to *PY_SSIZE_T_MIN* for a negative
-   integer or *PY_SSIZE_T_MAX* for a positive integer.
+   exception is cleared and the value is clipped to ``PY_SSIZE_T_MIN`` for a negative
+   integer or ``PY_SSIZE_T_MAX`` for a positive integer.
 
 
 .. c:function:: int PyIndex_Check(PyObject *o)