* _PyPreConfig_Write() now sets the memory allocator.
* _PyPreConfig_Write() gets a return type: _PyInitError.
* _Py_InitializeCore() now reads and writes the pre-configuration
(set the memory allocator, configure the locale) before reading and
writing the core configuration.
The development mode now uses the effective name of the debug memory
allocator ("pymalloc_debug" or "malloc_debug"). So the name doesn't
change after setting the memory allocator.
* Move 'allocator' and 'dev_mode' fields from _PyCoreConfig
to _PyPreConfig.
* Fix InitConfigTests of test_embed: dev_mode sets allocator to
"debug", add a new tests for env vars with dev mode enabled.
* Move following fields from _PyCoreConfig to _PyPreConfig:
* coerce_c_locale
* coerce_c_locale_warn
* legacy_windows_stdio
* utf8_mode
* _PyPreConfig_ReadFromArgv() is now responsible to choose the
filesystem encoding
* _PyPreConfig_Write() now sets the LC_CTYPE locale
* Add _PyPreConfig structure
* Move 'ignored' and 'use_environment' fields from _PyCoreConfig
to _PyPreConfig
* Add a new "_PyPreConfig preconfig;" field to _PyCoreConfig
