Remove UNTESTED_CORE_CONFIG from test_embed.InitConfigTests: all core
config fields are now tested!

Changes:

* Test also dll_path on Windows
* Add run_main_config unit test: test config using _Py_RunMain().

test_embed: add test_init_read_set() to test newly added APIs: test
module_search_paths and executable.

Clarify how to capture stdout and stderr combined into one stream.

Python 3.8 now respects the x86-64 ABI: memory allocations are
aligned on 16 bytes. The clang flag was only used as a temporary
workaround.

Argparse can handle default value as stdin and stdout for parameters
as file type (infile, outfile).

Replace global configuration variables with core_config read from the
current interpreter.

Cleanup dynload_hpux.c.

When using multiprocessing (-jN option), worker processes now create
their temporary directory inside the temporary directory of the
main process. So the main process is able to remove temporary
directories of worker processes even if they crash or when they are
killed by regrtest on KeyboardInterrupt (CTRL+c).

Rework also how multiprocessing arguments are parsed in main.py.

This cleans the csv module a bit, I don't think it requires a bpo issue or a news entry.

Removes more legacy distutils documentation, and more clearly
marks what is left as potentially outdated, with references to
setuptools as a replacement.

Add a new pip install before `sphinx` etc.. because we should use the last version of `pip` and `setuptools`

MultiprocessThread.kill() now closes stdout and stderr to prevent
popen.communicate() to hang.

* Update timeit.rst

* Docs: Add bz2 usage examples

- Adds an "Examples of usage" section inspired by the one
  found in the gzip docs
- Corrects the descriptions for ``compresslevel`` and ``data``:
    - ``compresslevel`` must be an `int`, not any number.  For
      instance, passing a float will raise ``TypeError``
    - Notes that `data` must be bytes-like

Followup to bpo-36867.

"python3 -m test -jN ..." now continues the execution of next tests
when a worker process crash (CHILD_ERROR state). Previously, the test
suite stopped immediately. Use --failfast to stop at the first error.

Moreover, --forever now also implies --failfast.

Move _PyImportZip_Init() to the internal C API and add an 'interp'
parameter.

https://bugs.python.org/issue34682

Remove the PyEval_ReInitThreads() function from the Python C API.
It should not be called explicitly: use PyOS_AfterFork_Child()
instead.

Rename PyEval_ReInitThreads() to _PyEval_ReInitThreads() and add a
'runtime' parameter.

Remove cp65001 from the codecs table, list it as an alias of utf_8
and add a versionchanged markup.

Co-Authored-By: Filip Gruszczyński <gruszczy@gmail.com>
Co-Authored-By: Michele Orrù <maker@tumbolandia.net>