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* Add support for Python 3.7 and 3.8 (adding to test matrix).
* Update development requirements.
* State machine names should now be fully qualified for mixins, simple names are deprecated and
  will no longer be supported on a future version.
* Development: Adding mypy linter.
* Add support for State machine inheritance. Thanks @rschrader.
* Add support for reverse transitions: ``transition = state_a.from_(state_b)``.
  Thanks @romulorosa.
* Fix current state equal to destination on enter events. Thanks @robnils and @joshuacc1.

Breaking changes:

* Drop official support for Python 3.4 (removing from test matrix, code may still work).