bpo-36763: Implement the PEP 587 (GH-13592)

* Add a whole new documentation page:
  "Python Initialization Configuration"
* PyWideStringList_Append() return type is now PyStatus,
  instead of int
* PyInterpreterState_New() now calls PyConfig_Clear() if
  PyConfig_InitPythonConfig() fails.
* Rename files:

  * Python/coreconfig.c => Python/initconfig.c
  * Include/cpython/coreconfig.h => Include/cpython/initconfig.h
  * Include/internal/: pycore_coreconfig.h => pycore_initconfig.h

* Rename structures

  * _PyCoreConfig => PyConfig
  * _PyPreConfig => PyPreConfig
  * _PyInitError => PyStatus
  * _PyWstrList => PyWideStringList

* Rename PyConfig fields:

  * use_module_search_paths => module_search_paths_set
  * module_search_path_env => pythonpath_env

* Rename PyStatus field: _func => func
* PyInterpreterState: rename core_config field to config
* Rename macros and functions:

  * _PyCoreConfig_SetArgv() => PyConfig_SetBytesArgv()
  * _PyCoreConfig_SetWideArgv() => PyConfig_SetArgv()
  * _PyCoreConfig_DecodeLocale() => PyConfig_SetBytesString()
  * _PyInitError_Failed() => PyStatus_Exception()
  * _Py_INIT_ERROR_TYPE_xxx enums => _PyStatus_TYPE_xxx
  * _Py_UnixMain() => Py_BytesMain()
  * _Py_ExitInitError() => Py_ExitStatusException()
  * _Py_PreInitializeFromArgs() => Py_PreInitializeFromBytesArgs()
  * _Py_PreInitializeFromWideArgs() => Py_PreInitializeFromArgs()
  * _Py_PreInitialize() => Py_PreInitialize()
  * _Py_RunMain() => Py_RunMain()
  * _Py_InitializeFromConfig() => Py_InitializeFromConfig()
  * _Py_INIT_XXX() => _PyStatus_XXX()
  * _Py_INIT_FAILED() => _PyStatus_EXCEPTION()

* Rename 'err' PyStatus variables to 'status'
* Convert RUN_CODE() macro to config_run_code() static inline function
* Remove functions:

  * _Py_InitializeFromArgs()
  * _Py_InitializeFromWideArgs()
  * _PyInterpreterState_GetCoreConfig()
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 0aa5e4a..0fe7b56 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -40,7 +40,7 @@
 
 #define PY_SSIZE_T_CLEAN
 #include "Python.h"
-#include "pycore_coreconfig.h"
+#include "pycore_initconfig.h"
 #include "pycore_fileutils.h"
 #include "pycore_object.h"
 #include "pycore_pylifecycle.h"
@@ -3549,9 +3549,9 @@
                                    interp->fs_codec.errors);
     }
     else {
-        const _PyCoreConfig *config = &interp->core_config;
+        const wchar_t *filesystem_errors = interp->config.filesystem_errors;
         _Py_error_handler errors;
-        errors = get_error_handler_wide(config->filesystem_errors);
+        errors = get_error_handler_wide(filesystem_errors);
         assert(errors != _Py_ERROR_UNKNOWN);
         return unicode_encode_utf8(unicode, errors, NULL);
     }
@@ -3567,9 +3567,9 @@
                                          interp->fs_codec.errors);
     }
     else {
-        const _PyCoreConfig *config = &interp->core_config;
+        const wchar_t *filesystem_errors = interp->config.filesystem_errors;
         _Py_error_handler errors;
-        errors = get_error_handler_wide(config->filesystem_errors);
+        errors = get_error_handler_wide(filesystem_errors);
         assert(errors != _Py_ERROR_UNKNOWN);
         return unicode_encode_locale(unicode, errors, 0);
     }
@@ -3787,9 +3787,9 @@
                                    NULL);
     }
     else {
-        const _PyCoreConfig *config = &interp->core_config;
+        const wchar_t *filesystem_errors = interp->config.filesystem_errors;
         _Py_error_handler errors;
-        errors = get_error_handler_wide(config->filesystem_errors);
+        errors = get_error_handler_wide(filesystem_errors);
         assert(errors != _Py_ERROR_UNKNOWN);
         return unicode_decode_utf8(s, size, errors, NULL, NULL);
     }
@@ -3805,9 +3805,9 @@
                                 interp->fs_codec.errors);
     }
     else {
-        const _PyCoreConfig *config = &interp->core_config;
+        const wchar_t *filesystem_errors = interp->config.filesystem_errors;
         _Py_error_handler errors;
-        errors = get_error_handler_wide(config->filesystem_errors);
+        errors = get_error_handler_wide(filesystem_errors);
         return unicode_decode_locale(s, size, errors, 0);
     }
 #endif
@@ -15200,7 +15200,7 @@
 
 /* Initialize the Unicode implementation */
 
-_PyInitError
+PyStatus
 _PyUnicode_Init(void)
 {
     /* XXX - move this array to unicodectype.c ? */
@@ -15218,12 +15218,12 @@
     /* Init the implementation */
     _Py_INCREF_UNICODE_EMPTY();
     if (!unicode_empty) {
-        return _Py_INIT_ERR("Can't create empty string");
+        return _PyStatus_ERR("Can't create empty string");
     }
     Py_DECREF(unicode_empty);
 
     if (PyType_Ready(&PyUnicode_Type) < 0) {
-        return _Py_INIT_ERR("Can't initialize unicode type");
+        return _PyStatus_ERR("Can't initialize unicode type");
     }
 
     /* initialize the linebreak bloom filter */
@@ -15232,15 +15232,15 @@
         Py_ARRAY_LENGTH(linebreak));
 
     if (PyType_Ready(&EncodingMapType) < 0) {
-         return _Py_INIT_ERR("Can't initialize encoding map type");
+         return _PyStatus_ERR("Can't initialize encoding map type");
     }
     if (PyType_Ready(&PyFieldNameIter_Type) < 0) {
-        return _Py_INIT_ERR("Can't initialize field name iterator type");
+        return _PyStatus_ERR("Can't initialize field name iterator type");
     }
     if (PyType_Ready(&PyFormatterIter_Type) < 0) {
-        return _Py_INIT_ERR("Can't initialize formatter iter type");
+        return _PyStatus_ERR("Can't initialize formatter iter type");
     }
-    return _Py_INIT_OK();
+    return _PyStatus_OK();
 }
 
 /* Finalize the Unicode implementation */
@@ -15718,23 +15718,23 @@
 }
 
 
-static _PyInitError
+static PyStatus
 init_stdio_encoding(PyInterpreterState *interp)
 {
     /* Update the stdio encoding to the normalized Python codec name. */
-    _PyCoreConfig *config = &interp->core_config;
+    PyConfig *config = &interp->config;
     if (config_get_codec_name(&config->stdio_encoding) < 0) {
-        return _Py_INIT_ERR("failed to get the Python codec name "
+        return _PyStatus_ERR("failed to get the Python codec name "
                             "of the stdio encoding");
     }
-    return _Py_INIT_OK();
+    return _PyStatus_OK();
 }
 
 
 static int
 init_fs_codec(PyInterpreterState *interp)
 {
-    _PyCoreConfig *config = &interp->core_config;
+    PyConfig *config = &interp->config;
 
     _Py_error_handler error_handler;
     error_handler = get_error_handler_wide(config->filesystem_errors);
@@ -15778,31 +15778,31 @@
 }
 
 
-static _PyInitError
+static PyStatus
 init_fs_encoding(PyInterpreterState *interp)
 {
     /* Update the filesystem encoding to the normalized Python codec name.
        For example, replace "ANSI_X3.4-1968" (locale encoding) with "ascii"
        (Python codec name). */
-    _PyCoreConfig *config = &interp->core_config;
+    PyConfig *config = &interp->config;
     if (config_get_codec_name(&config->filesystem_encoding) < 0) {
-        return _Py_INIT_ERR("failed to get the Python codec "
+        return _PyStatus_ERR("failed to get the Python codec "
                             "of the filesystem encoding");
     }
 
     if (init_fs_codec(interp) < 0) {
-        return _Py_INIT_ERR("cannot initialize filesystem codec");
+        return _PyStatus_ERR("cannot initialize filesystem codec");
     }
-    return _Py_INIT_OK();
+    return _PyStatus_OK();
 }
 
 
-_PyInitError
+PyStatus
 _PyUnicode_InitEncodings(PyInterpreterState *interp)
 {
-    _PyInitError err = init_fs_encoding(interp);
-    if (_Py_INIT_FAILED(err)) {
-        return err;
+    PyStatus status = init_fs_encoding(interp);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
     }
 
     return init_stdio_encoding(interp);
@@ -15814,7 +15814,7 @@
 _PyUnicode_EnableLegacyWindowsFSEncoding(void)
 {
     PyInterpreterState *interp = _PyInterpreterState_GET_UNSAFE();
-    _PyCoreConfig *config = &interp->core_config;
+    PyConfig *config = &interp->config;
 
     /* Set the filesystem encoding to mbcs/replace (PEP 529) */
     wchar_t *encoding = _PyMem_RawWcsdup(L"mbcs");