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* Added support for Python 3.6, 3.7.
* Dropped support for Python 2.6, 3.2 - 3.4. They may still work, no promises.
* Renamed DEFAULT_ALOGRITHM to DEFAULT_ALGORITHM
* Renamed b58_digest arguments to b64digest
* Added Hash.b64digest
* Added type checking to Hash.__init__() arguments
* Added docstrings and doctests to Hash methods