Treat an argument of "--help" as a request to print help, instead of a filename
to add to the source lists.
Treat the arguments "src/foo.cpp" "src/foo.hpp" as two filenames, instead of
adding src/foo.cpp to target src/foo.hpp. The old command line
./add_source_file a b c
becomes
./add_source_file a --target b --target c
When saying that pbxproj is required, suggest optionally using a venv instead
of installing systemwide.
Usage: ./add_source_file <filename> [target ...]
Targets are "wesnoth", "wesnothd", "campaignd", "lua", "tests".
It defaults to the "wesnoth" target.
The 'pbxproj' python package is required to modify the Xcode project.
[ci skip]
