• Added cache service

Patched list operation on base.Manager

• Updated retry random generation

• Added Retry constructor

• Optimized list operation

• Update storage.Storager interface
  • Delete with options
  • Exists with options
• Renamed option.Obejct to option.ObjectKind

• Added option.Object

• Added Storager.Get(ctx context.Context, location string, options ...Option) (os.FileInfo, error) interface
• Added Getter.Object(ctx context.Context, URL string, options ...Option) (Object, error) interface
• Optimize Exists, Object operation (to avoid expensive list operation)
• Added base.Storager

• Added generation option