func NewCache(diskRoot string) *Cache {
	return &Cache{
		diskRoot: strings.TrimSuffix(diskRoot, string(os.PathListSeparator)),
	}
}
func NewCache(diskRoot string) *Cache {
	return &Cache{
		diskRoot: strings.TrimSuffix(diskRoot, string(os.PathListSeparator)),
	}
}
// NewCache returns a new Cache given the root directory that should be used
// on disk for cache storage