Make get/put more robust

- init folder if not present already in 'get()' call
  - put.go was referencing wrong args - fix it
  - if no OBJECTNAME is specified during 'get' - grab a
    list of files under "~/.minio"
  - Provide new API GetList() for ObjectStorage struct

pkgs/storage/storage.go

@@ -1,6 +1,7 @@
 package storage
 
 type ObjectStorage interface {
+	GetList() ([]byte, error)
 	Get(path string) ([]byte, error)
 	Put(path string, object []byte) error
 }