Each interpreter now has its own empty bytes string and single byte
character singletons.
Replace STRINGLIB_EMPTY macro with STRINGLIB_GET_EMPTY() macro.
The public API symbols being removed are:
_PyBytes_InsertThousandsGroupingLocale, _PyBytes_InsertThousandsGrouping, _Py_InitializeFromArgs, _Py_InitializeFromWideArgs, _PyFloat_Repr, _PyFloat_Digits,
_PyFloat_DigitsInit, PyFrame_ExtendStack, _PyAIterWrapper_Type, PyNullImporter_Type, PyCmpWrapper_Type, PySortWrapper_Type, PyNoArgsFunction.
* Decode thousands separator and decimal point using PyUnicode_DecodeLocale()
(from the locale encoding), instead of decoding them implicitly from latin1
* Remove _PyUnicode_InsertThousandsGroupingLocale(), it was not used
* Change _PyUnicode_InsertThousandsGrouping() API to return the maximum
character if unicode is NULL
* Replace MIN/MAX macros by Py_MIN/Py_MAX
* stringlib/undef.h undefines STRINGLIB_IS_UNICODE
* stringlib/localeutil.h only supports Unicode