Pyevtk

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* Brings this repo in sync with Paulo Herrera's old BitBucket and new GitHub
* Adds some new examples and fixes some compatibility issues with != None
* Vector image support for imagetoVTK
* Adds more tests to CI
* Adds "evtk" package (identical to "pyevtk") for backward compatibility with
depricated warning

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* Makes sdist installable update CI infrastructure

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* Added unit-tests and Travis-CI integration.

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* Added Python3-compatible relative imports (PR by Rene Milk).

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* Ported over latest changes made in the original repo by Paulo Herrera.

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* First port of the original PyEVTK by Paulo Herrera.