Keyrings.cryptfile

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- Fix showstopper, introduced by 1.3.1 changes

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- Fix PyPI description formatting

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- Fix install issues, if keyring isn''t installed beforehand.
Thanks, Erik.

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- Compatibility with keyring 15. Thanks, Niklas.
- Add note about keyring_key. Thanks, Wade.
- Clean up setup.py, fetch version from cryptfile

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- Flag markdown readme correctly in setup (for PyPI).

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- Keyrings namespace package has switched from pkg_resources
to pkgutil for native namespace package support. Thanks, Jason.
- adjust copyright year in license
- be more specific about python versions