Support ed25519 whenever possible - RFC DRAFT

[northox]

Follow

https://bugzilla.mindrot.org/show_bug.cgi?id=2197

http://tools.ietf.org/html/draft-moonesamy-sshfp-ed25519-01

[northox]

Seems like IANA use number 4 as identifier.

[northox]

Fixed by #4