Allow future-proof initialisation of Py_CoreConfig

pep-0432.txt

@@ -546,9 +546,16 @@ configuration::
         unsigned long hash_seed;
     } Py_CoreConfig;
 
+    #define Py_CoreConfig_INIT {0, -1, 0}
+
 The core configuration settings pointer may be ``NULL``, in which case the
 default values are ``ignore_environment = 0`` and ``use_hash_seed = -1``.
 
+The ``Py_CoreConfig_INIT`` macro is designed to allow easy initialization
+of a struct instance with sensible defaults::
+
+    Py_CoreConfig core_config = Py_CoreConfig_INIT;
+
 ``ignore_environment`` controls the processing of all Python related
 environment variables. If the flag is zero, then environment variables are
 processed normally. Otherwise, all Python-specific environment variables