Proper FTP archiving support

[Arkiver2]

While FTP download is well supported in Wget, support for FTP archiving is not optimal, especially when it comes to listings and recording communication with the FTP server.

Proper FTP archiving should follow Heritrix specifications at https://web.archive.org/web/20161013220251/http://aaron.blog.archive.org/2013/05/17/handling-archived-ftp-resources/.

[Arkiver2]

Initial support is in the ftp branch https://github.com/ArchiveTeam/wget-lua/tree/ftp.