bpo-42236: Enhance init and encoding documentation (GH-23109)

Enhance the documentation of the Python startup, filesystem encoding
and error handling, locale encoding. Add a new "Python UTF-8 Mode"
section.

* Add "locale encoding" and "filesystem encoding and error handler"
  to the glossary
* Remove documentation from Include/cpython/initconfig.h: move it to
  Doc/c-api/init_config.rst.
* Doc/c-api/init_config.rst:

  * Document command line options and environment variables
  * Document default values.

* Add a new "Python UTF-8 Mode" section in Doc/library/os.rst.
* Add warnings to Py_DecodeLocale() and Py_EncodeLocale() docs.
* Document how Python selects the filesystem encoding and error
  handler at a single place: PyConfig.filesystem_encoding and
  PyConfig.filesystem_errors.
* PyConfig: move orig_argv member at the right place.

1 files changed, 5 insertions, 5 deletions

diff --git a/Doc/howto/unicode.rst b/Doc/howto/unicode.rst
index e948c1e..535b21b 100644
--- a/Doc/howto/unicode.rst
+++ b/Doc/howto/unicode.rst
@@ -609,9 +609,9 @@ implemented by converting the Unicode string into some encoding that
 varies depending on the system.  Today Python is converging on using
 UTF-8: Python on MacOS has used UTF-8 for several versions, and Python
 3.6 switched to using UTF-8 on Windows as well.  On Unix systems,
-there will only be a filesystem encoding if you've set the ``LANG`` or
-``LC_CTYPE`` environment variables; if you haven't, the default
-encoding is again UTF-8.
+there will only be a :term:`filesystem encoding <filesystem encoding and error
+handler>`. if you've set the ``LANG`` or ``LC_CTYPE`` environment variables; if
+you haven't, the default encoding is again UTF-8.
 
 The :func:`sys.getfilesystemencoding` function returns the encoding to use on
 your current system, in case you want to do the encoding manually, but there's
@@ -633,8 +633,8 @@ provided the directory path as bytes or a Unicode string.  If you pass a
 Unicode string as the path, filenames will be decoded using the filesystem's
 encoding and a list of Unicode strings will be returned, while passing a byte
 path will return the filenames as bytes.  For example,
-assuming the default filesystem encoding is UTF-8, running the following
-program::
+assuming the default :term:`filesystem encoding <filesystem encoding and error
+handler>` is UTF-8, running the following program::
 
    fn = 'filename\u4500abc'
    f = open(fn, 'w')