Pytest-flake8

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- Allow running with no cacheprovider
- Modernize use of fixtures in tests

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- Added new options "flake8-max-complexity", "flake8-show-source"
and "flake8-statistics"

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- Update for flake8 3.x

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- Fix rendering of rST; from Ken Dreyer

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- Really fix cache usage; had a comparison between tuple and
list which always failed

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- Use integrated pytest cache instead of separate pytest-cache
module (which is now integrated)
- Use documented hooks for start and end of a test run