Tag to be used with the master branch of atlas/athena. Update(s) since 2.0.20: - Introduced fixes for AnalysisBaseExternals on Ubuntu and macOS; - Added FindCURL.cmake to AtlasLCG to be able to use CURL from the LCG releases if necessary; - Updated the code handling Doxygen to work successfully with LCG_94; - Added a lot of CMake changes to make the code work smoothly with CMake >=3.13.