Primarily motivated by issues on Mac when using app bundles - they default the working directory to / which means it's tricky for users to write cross-platform code with SFML, they either have to manually adjust the working directory or get the path to the app resources themselves.

Otherwise, these functions have a wide range of uses for the types of applications SFML users create - saving screenshots, user settings, loading user pictures, etc.

Influenced by how some other libraries offer the same, such as SDL

Purely additive API so could be a candidate for the next minor release