IO module now behaves according to issue #121.

[NOhs]

Apart from the changes in behaviour as described in issue #121, the new implementation

• gets rid of a lot of Path <-> str back and forth conversions,
• it removes duplicates by consistently using sets instead of manually cleaning up
• it tries to more closely use terminology used throughout the project
• it tries to split up the code into reasonable helper functions
• it tries to improve the expressiveness of the "main" function

[GPMueller]

Unfortunately some conflicts have appeared in 'clang_build/io_tools.py' in the meantime, which I'm not 100% sure how to fix correctly... Would be good to rebase this branch and check what the new CI says.

Edit: I think I merged correctly, but several tests are failing, including

• test_hello_world_mwe
• test_mwe_two_targets
• test_automatic_include_folders