First major version release! Major changes:
* Added support for Python 3.6+:
* Use `six` to write Python 2/3 compatible code
* Dropped `simplejson` dependency in favor of std lib `json` module
* Updated to build a universal wheel
* Added tests against Python 3.6 and 3.7 in Travis CI
* Improved dev tooling:
* Updated local venv to use Python 3.7
* Added `make deps` for regenerating `requirements.txt`
* Added `make format` for auto-formatting code
* Updated `make lint` to check Python 2/3 compatibility, import sorting
* Improved packaging:
* Moved dev requirements into `extras_require[dev]`
* Added classifiers, maintainer, `python_requires`
* Moved version into its own `VERSION` file