Derives a new key from the given resource-key. Only keys for a hierarchical storage system (like file-systems or URLs) can have derived keys. Since LibLoader 0.3.0 only hierarchical keys can be derived. For that, the deriving path must be given as String.
Before trying to derive the key, the system tries to interpret the path as absolute key-value.
@param parent the parent key, must never be null
@param path the relative path, that is used to derive the key.
@return the derived key.
@throws ResourceKeyCreationException if deriving the key failed.