v2.0.0 - It's Alive!

2.0.0

• export - register entities in a module's __all__ list
  (thanks @Paebbels!)
• Use of Decorator class and consistent callable signature for generic
  decorators is now required
• Drop support for Python <3.6
• Move to a src/ layout
• Lots of clarifications, typo fixes, and improvements to the docs
• Lots of development environment improvements:
  • Automatic distribution of tagged commits via PyPI (thanks @Paebbels!)
  • Makefile for a consistent interface into build operations
  • Improvements to tox configuration
  • Addition of consistent and required linting with pylint, mypy, and flake8
  • Autoformatting with black