Resolves #19

In order to easily add the package to PyPI, the package was migrated to poetry for easier dependency management and publishing.

The original package information was attempted to be retained, here's a quick summary of the changes:

• use semantic versioning (2.0.0.0 -> 2.0.0); allows use of poetry's version bumping
• add keywords and classifiers to the package for better PyPI searching
• dropped setup.py for poetry's use of pyproject.toml
  • introduce tox for easy testing and coverage commands; $ poetry run tox
  • consolidate .coveragerc and .pylintrc into tox.ini

At this point, all that should be necessary is running poetry publish.