Unihan-etl

- Major internal refactor and simplification
- Convert to pytest `assert` statements
- Convert full test suite to pytest functions and fixtures
- Get CLI documentation up again
- Improve test coverage
- Lint code, remove unused imports
- Switch license BSD -> MIT

- Rebooted
- Modernize _Makefile_ in docs
- Add Makefile to main project
- Modernize package metadata to use _**about**.py_
- Update requirements to use _requirements/_ folder for
base, testing and doc dependencies.
- Update sphinx theme to alabaster with new logo.
- Update travis to use coverall
- Update links on README to use https
- Update travis to test up to python 3.6
- Add support for pypy (why not)
- Lock base dependencies
- Add dev dependencies for isort, vulture and flake8

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