Pytest-splinter

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- handle exceptions during screenshot saving (blueyed, bubenkoff)
- documentation improvements (blueyed)

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- status_code is back in a lazy way (bubenkoff)

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- Fix automatic download of pdf content type (bubenkoff)

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- fix failing the test run if pytest-xdist is not installed, as it's completely optional dependency (bubenkoff, slafs)

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- improve exception handing when preparing the browser instance (bubenkoff)
- require pytest (bubenkoff)

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- automatic screenshot capture on test failure (bubenkoff)
- improvements to the browser preparation procedure (bubenkoff)
- boolean config options made more clear (bubenkoff)