Billiard

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- Issue 309: Add Python 3.9 support to spawnv_passfds()
- fix 314

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- Logging max memory reached at INFO rather than WARNING (255)

- Pass arguments when wrapping sys.exit (275)

- Remove win32/py2k special (276)

- Ensure READY messages sent out by exiting worker are consumed prior to it actually existing.

- Pass max_memory_per_child to child worker process (251)

- Fix compatibility with Python 2.7 on Windows (283)

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- Add support of sending parent process death signal.

- Previous fix for handling timeouts caused a problem in warm shutdowns due
to use of deepcopy.

We now use a shallow copy of the cache and do so only when it is needed.

- Cleanup old checks and workarounds for Python versions we no longer support.

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- Fix a crash when handling a timeout.
- Improve billiard.einfo.Frame compatibility with Python to avoid crashes when using Django.
- Cleanups.

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- Fix rebuild_ctype losing BufferedWrapper reference on Python 3.
- Deprecation warning with python 3.6 fixed.
- Correct spawn start method.

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- Adds Process._authkey alias to .authkey for 2.7 compat.
- Remove superfluous else clause from max_memory_per_child_check.
- Document and test all supported Python versions.
- Extend 'Process' to be compatible with < Py3.5.
- Use a properly initialized logger in pool.py error logging.
- _trywaitkill can now kill a whole process group if the worker process declares itself as a group leader.
- Fix cpython issue 14881 (See https://bugs.python.org/issue14881).
- Fix for a crash on windows.
- Fix messaging in case of worker exceeds max memory.