Reposition qfs to wrap the values package

[b5]

In concrete terms this means progressively enhancing the File interface to deal in value.Value:

type File interface {
  io.ReadCloser
	FileName() string
	FullPath() string
	IsDirectory() bool
	NextFile() (File, error)
  ModTime() time.Time
  Size()
  MediaType() string

  Value() interface{}
}

The goal is to eventually end here:

type File interface {
  Path() string
  Size() int64
  ModTime() time.Time
  MediaType() string

  Value() interface{}
}