Add the separator fix for the "values" loading as well
Throw Exception if sent path doesn't end in res

- Currently, if a path doesn't end in res directory, it will silently not fail in the load, but will fail when the resource is tried to be read. leading to confusion as to why it can't find a resource.
Added tests for PackageResourceLoader
Merge pull request #708 from SuperJugy/FileSeparatorFixes

Add the res folder enforcement to "values" and add check