[3.13] pythongh-141004: Document Py_MATH_{E, PI, TAU} constants (pythonGH-141373) (python#141472)

pythongh-141004: Document `Py_MATH_{E, PI, TAU}` constants (pythonGH-141373)
(cherry picked from commit f1330b3)

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>

Author: miss-islington

Doc/c-api/float.rst

@@ -96,16 +96,33 @@ Floating-Point Objects
    the C11 standard ``<math.h>`` header.
 
 
+.. c:macro:: Py_MATH_E
+
+   The definition (accurate for a :c:expr:`double` type) of the :data:`math.e` constant.
+
+
 .. c:macro:: Py_MATH_El
 
    High precision (long double) definition of :data:`~math.e` constant.
 
 
+.. c:macro:: Py_MATH_PI
+
+   The definition (accurate for a :c:expr:`double` type) of the :data:`math.pi` constant.
+
+
 .. c:macro:: Py_MATH_PIl
 
    High precision (long double) definition of :data:`~math.pi` constant.
 
 
+.. c:macro:: Py_MATH_TAU
+
+   The definition (accurate for a :c:expr:`double` type) of the :data:`math.tau` constant.
+
+   .. versionadded:: 3.6
+
+
 .. c:macro:: Py_RETURN_NAN
 
    Return :data:`math.nan` from a function.