Qt6 Documentation set: added documentation of 'additional libraries'. default tip

Updated copyright for 2021.

Added documentation set for Qt 6.0.

Deleted documentation sets for obsolete Python versions (3.4 and 3.5).

Updated the project file.

Added dosumentation set for Python 3.9.

Created global tag <release-2.0.0>.

Removed API files for Python2, PyQt4 and Qt4. release-2.0.0

Added QtHelp package for

Added QtHelp package for

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eric ide