Libusb

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- Drop support for Python 2
- Drop support for Python 3.4
- Add support for Python 3.8
- Setup update and cleanup.

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- Setup improvement.
- Update required setuptools version.
- Some updates of examples.

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- Setup improvement.
- Update required setuptools version.

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- Upgrade to the libusb v.1.0.22
- Setup improvement.

* Core: Refactor code related to transfer flags and timeout handling
* Darwin: Ignore root hub simulation devices
* Darwin: Improved support for OS X El Capitan
* Darwin: Work around devices with buggy endpoint descriptors
* Darwin: Do not use objc_registerThreadWithCollector after its deprecation
* Darwin: Use C11 atomics on 10.12+ as the OS atomics are now deprecated
* Linux: Support preallocating kernel memory for zerocopy USB
* Linux: Deal with receiving POLLERR before all transfers have completed
* Solaris: Add solaris backend
* Windows: Add Visual Studio 2015 support
* Windows: Add usbdk backend
* Prevent attempts to recursively handle events
* Fix race condition in handle_timeout()
* Allow transferred argument to be optional in bulk APIs
* Various other bug fixes and improvements

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- Improve and simplify setup and packaging.