Maildir-deduplicate

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* Add Python 3.4 and 3.5 support. Closes 30.
* Add default ``isort`` configuration.
* Remove hackish default encoding forcing in main code.

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* Fix ``AttributeError`` on message instance. Closes 28.
* Various fixes of references to internal variables introduced
by a switch to more Pythonic classes in 1.0.0.
* Remove ``Message-ID`` from the list of default canonical headers.

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* Switch from coveralls.io to codecov.io.

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* Fix package version parsing.
* Add installation instructions. Closes 21.
* Add PEP8 and PyLint configuration.
* Add bumpversion configuration.
* Rework CLI around click framework. Closes 26.

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* Package the script for proper distribution.

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* First external contribution.