Fix static_store with relative paths

Fixes two issues:

 - The first element when you call `resource_package!` is a `Path`, which can be either a `posix::Path` or a `windows::Path`, depending on the compilation platform (this is due to technical reasons)

 - People may want to call `resource_package!(../../my_resources/*)`, in which case all the paths would start with `../../` ; that's why you need `ends_with_path` instead of a simple comparaison