--follow-metalink=true|false|mem If true or mem is specified, when a file
whose suffix is .meta4 or .metalink, or content
type of application/metalink4+xml or
application/metalink+xml is downloaded, aria2
parses it as a metalink file and downloads files
mentioned in it.
If mem is specified, a metalink file is not
written to the disk, but is just kept in memory.
If false is specified, the .metalink file is
downloaded to the disk, but is not parsed as a
metalink file and its contents are not
downloaded.