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* s5p_plot.py [draw_qhist]: added grid-lines and denisty parameter, improved axis labels
* Rearranged source tree to comply with PIP 517, 518 (requires: setuptools 42 or later)
* Renamed lib.sw_version.py to version.py
* Removed all test-modules and examples because these are obsolete. Will be replaced by up-to-date code in future commits
* Fixed pylint warnings
* Updated Copyright line in all modules
* Updated files INSTALL and README
* Added ToDo, which contains a listing of new functionality to be implemented before a new minor release
* Added ChangeLog