* 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()

* _PyPreConfig_GetGlobalConfig() and  _PyCoreConfig_GetGlobalConfig()
  now do nothing if the configuration was not initialized with
  _PyPreConfig_InitCompatConfig() and _PyCoreConfig_InitCompatConfig()
* Remove utf8_mode=-2 special case: use utf8_mode=-1 instead.
* Fix _PyPreConfig_InitPythonConfig():

  * isolated = 0 instead of -1
  * use_environment = 1 instead of -1

* Rename _PyConfig_INIT to  _PyConfig_INIT_COMPAT
* Rename _PyPreConfig_Init() to _PyPreConfig_InitCompatConfig()
* Rename _PyCoreConfig_Init() to _PyCoreConfig_InitCompatConfig()
* PyInterpreterState_New() now uses _PyCoreConfig_InitPythonConfig()
  as default configuration, but it's very quickly overriden anyway.
* _freeze_importlib.c uses _PyCoreConfig_SetString() to set
  program_name.
* Cleanup preconfig_init_utf8_mode(): cmdline is always non-NULL.

_PyPreConfig_InitPythonConfig() and _PyCoreConfig_InitPythonConfig()
no longer inherit their values from global configuration variables.

Changes:

* _PyPreCmdline_Read() now ignores -X dev and PYTHONDEVMODE
  if dev_mode is already set.
* Inline _PyPreConfig_INIT macro into _PyPreConfig_Init() function.
* Inline _PyCoreConfig_INIT macro into _PyCoreConfig_Init() function.
* Replace _PyCoreConfig_Init() with _PyCoreConfig_InitPythonConfig()
  in most tests of _testembed.c.
* Replace _PyCoreConfig_Init() with _PyCoreConfig_InitIsolatedConfig()
  in _freeze_importlib.c.
* Move some initialization functions from the internal
  to the private API.

* Add _PyInitError functions:

  * _PyInitError_Ok()
  * _PyInitError_Error()
  * _PyInitError_NoMemory()
  * _PyInitError_Exit()
  * _PyInitError_IsError()
  * _PyInitError_IsExit()
  * _PyInitError_Failed()

* frozenmain.c and _testembed.c now use functions rather than macros.
* Move _Py_INIT_xxx() macros to the internal API.
* Move _PyWstrList_INIT macro to the internal API.

Add new functions to get the Python interpreter behavior:

* _PyPreConfig_InitPythonConfig()
* _PyCoreConfig_InitPythonConfig()

Add new functions to get an isolated configuration:

* _PyPreConfig_InitIsolatedConfig()
* _PyCoreConfig_InitIsolatedConfig()

Replace _PyPreConfig_INIT and _PyCoreConfig_INIT with new functions
_PyPreConfig_Init() and _PyCoreConfig_Init().

_PyCoreConfig: set configure_c_stdio and parse_argv to 0 by default
to behave as Python 3.6 in the default configuration.

_PyCoreConfig_Read() no longer sets coerce_c_locale_warn to 1 if it's
equal to 0. coerce_c_locale_warn must now be set to -1 (ex: using
_PyCoreConfig_InitPythonConfig()) to enable C locale coercion
warning.

Add unit tests for _PyCoreConfig_InitPythonConfig()
and _PyCoreConfig_InitIsolatedConfig().

Changes:

* Rename _PyCoreConfig_GetCoreConfig() to _PyPreConfig_GetCoreConfig()
* Fix core_read_precmdline(): handle parse_argv=0
* Fix _Py_PreInitializeFromCoreConfig(): pass coreconfig.argv
  to _Py_PreInitializeFromPyArgv(), except if parse_argv=0

* Add a private _Py_InitializeMain() function.
* Add again _PyCoreConfig._init_main.
* _Py_InitializeFromConfig() now uses _init_main to decide
  if _Py_InitializeMainInterpreter() should be called.
* _PyCoreConfig: rename _frozen to pathconfig_warnings, its value is
  now the opposite of Py_FrozenFlag.
* Add an unit test for _init_main=0 and _Py_InitializeMain().

* Remove _PyInitError.user_err field and _Py_INIT_USER_ERR() macro:
  use _Py_INIT_ERR() instead. _Py_ExitInitError() now longer calls
  abort() on error: exit with exit code 1 instead.
* Add _PyInitError._type private field.
* exitcode field type is now unsigned int on Windows.
* Rename prefix field to _func.
* Rename msg field to err_msg.

* Add _PyCoreConfig._init_main: if equals to zero,
  _Py_InitializeFromConfig() doesn't call
  _Py_InitializeMainInterpreter().
* Add interp_p parameter to _Py_InitializeFromConfig().
* pymain_init() now calls _Py_InitializeFromConfig().
* Make _Py_InitializeCore() private.

Add a new _Py_INIT_EXIT() macro to be able to exit Python with an
exitcode using _PyInitError API. Rewrite function calls by
pymain_main() to use _PyInitError.

Changes:

* Remove _PyMain.err and _PyMain.status field
* Add _Py_INIT_EXIT() macro and _PyInitError.exitcode field.
* Rename _Py_FatalInitError() to _Py_ExitInitError().