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* supporting only python 3.7+
* fix 10: Memory leak in DirectedHeuristicGraph
* fix BUG where "dangling" extremities in the visibility graph would be deleted
* using generators to refer to the polygon properties (vertices,...) of an environment (save memory and remove redundancy)
* enabled plotting the test results, at the same time this is testing the plotting functionality
* added typing
internal:
* added sphinx documentation, included auto api documentation, improved docstrings
* added contribution guidelines
* add sponsor button
* updated publishing routine
* split up requirement files (basic, tests)
* specific tags for supported python versions in wheel
* testing all different python versions with tox
* added coverage tests
* added editorconfig
* specify version in VERSION file
* added new tests