Mention public macros in docs

Author: skirpichev

Doc/library/stdtypes.rst

@@ -723,7 +723,8 @@ made available to Python as the :attr:`modulus` attribute of
 .. impl-detail::
 
    Currently, the prime used is ``P = 2**31 - 1`` on machines with 32-bit C
-   longs and ``P = 2**61 - 1`` on machines with 64-bit C longs.
+   longs and ``P = 2**61 - 1`` on machines with 64-bit C longs.  The exponent
+   of this Mersenne prime is available as ``_PyHASH_BITS`` macro.
 
 Here are the rules in detail:
 

Doc/library/sys.rst

@@ -1022,19 +1022,22 @@ always available.
 
    .. attribute:: hash_info.modulus
 
-      The prime modulus P used for numeric hash scheme
+      The prime modulus P used for numeric hash scheme.  Available also as
+      ``_PyHASH_MODULUS`` macro.
 
    .. attribute:: hash_info.inf
 
-      The hash value returned for a positive infinity
+      The hash value returned for a positive infinity.  Available also as
+      ``_PyHASH_INF`` macro.
 
    .. attribute:: hash_info.nan
 
       (This attribute is no longer used)
 
    .. attribute:: hash_info.imag
 
-      The multiplier used for the imaginary part of a complex number
+      The multiplier used for the imaginary part of a complex number.
+      Available also as ``_PyHASH_IMAG`` macro.
 
    .. attribute:: hash_info.algorithm