Add support for Ed25519 keys.

lib/Net/SSH/AuthorizedKey/SSH2.pm: add support for the "ssh-ed25519" prefix
t/002Ssh-2.t: test processing t/canned/ak-ed25519.txt
t/canned/ak-ed25519.txt: authorized_keys test case
Merge pull request #1 from dlg-yahoo/master

Add support for Ed25519 keys