Pyramid-sawing

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- Adjust the transit logging tween to set and return the response attribute
of the request object.
- Fix tests for Python3 compatiblity.

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- Fix the transit logging tween to return the response coming from
the handler rather than the one attached to the request object. [pumazi]

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- Fix the transit logging tween by returning the response,
which caused secondary tweens and event subscribers to fail. [pumazi]

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- Add a transit (request) logging feature that mimics functionality
found in ``pyramid_translogger``. [pumazi]

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- Add a logging filter that allows for ``%(hostname)s`` be be used
within log lines. [pumazi]
- Logging from a YAML file. [pumazi]