FileManager additions to simplify access to iOS app sandbox.
let cachesDir = FileManager.default.fu_cachesDir()
let libraryDir = FileManager.default.fu_libraryDir()
if let path = try? FileManager.default.fu_documentSubDir(withComponent: "MyFiles") {
print("\(path)")
}
do {
let path = try FileManager.default.fu_persistentAppDataPath()
print("\(path)")
} catch {
print("\(error)")
}