Add support for ecdsa and ed25519 keys

[claudijd]

Fixes #486

Example output changes:

"keys": {
  "ecdsa-sha2-nistp256": {
    "raw": "ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBC4gXA5naQtjcKu90NJ7A4jQ1UgxYGdnndJyr4PSZJ59qJUzkoH3VgdTlseXbIZHwO4k2gNcFpaMq5gqVRobAwU=",
    "length": 520,
    "fingerprints": {
      "md5": "be:04:32:74:c6:63:fa:24:c3:c6:78:c2:cd:d2:3e:f4",
      "sha1": "00:67:e3:4d:78:2f:65:94:87:bf:54:5a:1e:92:af:67:0b:8d:b5:2c",
      "sha256": "EZe8ZoSwAzDOLR45H2PZ1aGGfnt59ZLrL5bwnjQwTUI="
    }
  },
  "rsa": {
    "raw": "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCl/BNLUxR49+3AKqhf6sWKrh8XXzqXV00bEPFtcJFWxyRqC5pPWo9zRRiS2jitIcqljIQVohEEZHt48vZaA1hniVfe/FmrFzuCOuQOIP2fuRgLSNHu+lWVScsHoX/MuYXEIxj6aW7UpFn4lD01mvPtazXFO/tJ+LRs49YBP7UvL1smIS2xoyuH7kZDN17QG08YwbIB2fApMl8rXH+2Rpj5hlv+7rcZ1dqCGtmXmvsv8fKGYd7BxRy0s/d7EY4e/DeDxA1qTNV9BrBTNn6jAKIedTE5s4GNRbN/Q20mP2qmw70PiTGROw6xp9SBFA7N9hjjOT7iutK/pa7y1joXKjeJ",
    "length": 2048,
    "fingerprints": {
      "md5": "fc:c5:5b:0d:f0:c6:fd:fe:80:18:62:2c:05:38:20:8a",
      "sha1": "e1:3c:71:49:80:37:87:32:b5:0c:e3:86:41:ef:2e:2a:2f:14:e3:58",
      "sha256": "aH0wN2cs6x5Ktf9PvIzoQeFVqDBC4I484wq6vNv9XFA="
    }
  },
  "ed25519": {
    "raw": "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAINO+ybidO9DGOb1dDwyVvGcrCD/wILFWTYtWUQZVxXwH",
    "length": 256,
    "fingerprints": {
      "md5": "0f:db:50:54:15:22:b3:6f:31:7c:ee:22:23:77:bc:77",
      "sha1": "32:d1:e8:50:ae:1c:cb:11:c5:09:fa:02:6e:f4:e8:dc:11:11:4c:48",
      "sha256": "p+P78wR61KZ4UvQZpr84EqslnRkhZ7txT1bN8vA/oHU="
    }
  }
},