[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/conversion.rst b/Doc/c-api/conversion.rst
index c02fa60..b310fcb 100644
--- a/Doc/c-api/conversion.rst
+++ b/Doc/c-api/conversion.rst
@@ -32,7 +32,7 @@
 
 If the platform doesn't have :c:func:`vsnprintf` and the buffer size needed to
 avoid truncation exceeds *size* by more than 512 bytes, Python aborts with a
-*Py_FatalError*.
+:c:func:`Py_FatalError`.
 
 The return value (*rv*) for these functions should be interpreted as follows:
 
@@ -95,21 +95,21 @@
    must be 0 and is ignored.  The ``'r'`` format code specifies the
    standard :func:`repr` format.
 
-   *flags* can be zero or more of the values *Py_DTSF_SIGN*,
-   *Py_DTSF_ADD_DOT_0*, or *Py_DTSF_ALT*, or-ed together:
+   *flags* can be zero or more of the values ``Py_DTSF_SIGN``,
+   ``Py_DTSF_ADD_DOT_0``, or ``Py_DTSF_ALT``, or-ed together:
 
-   * *Py_DTSF_SIGN* means to always precede the returned string with a sign
+   * ``Py_DTSF_SIGN`` means to always precede the returned string with a sign
      character, even if *val* is non-negative.
 
-   * *Py_DTSF_ADD_DOT_0* means to ensure that the returned string will not look
+   * ``Py_DTSF_ADD_DOT_0`` means to ensure that the returned string will not look
      like an integer.
 
-   * *Py_DTSF_ALT* means to apply "alternate" formatting rules.  See the
+   * ``Py_DTSF_ALT`` means to apply "alternate" formatting rules.  See the
      documentation for the :c:func:`PyOS_snprintf` ``'#'`` specifier for
      details.
 
-   If *ptype* is non-NULL, then the value it points to will be set to one of
-   *Py_DTST_FINITE*, *Py_DTST_INFINITE*, or *Py_DTST_NAN*, signifying that
+   If *ptype* is non-``NULL``, then the value it points to will be set to one of
+   ``Py_DTST_FINITE``, ``Py_DTST_INFINITE``, or ``Py_DTST_NAN``, signifying that
    *val* is a finite number, an infinite number, or not a number, respectively.
 
    The return value is a pointer to *buffer* with the converted string or