RSA and ECDSA keys should be encoded as a PEM string

[erickt]

According to the spec section 4.2, "rsa" and "ecdsa" keys, as defined by:

  { "keytype" : "rsa",
    "scheme" : "rsassa-pss-sha256",
    "keyval" : {"public" : PUBLIC}
  }

  { "keytype" : "ecdsa-sha2-nistp256",
    "scheme" : "ecdsa-sha2-nistp256",
    "keyval" : {"public" : PUBLIC}
  }

The public portion of the key should be encoded as a PEM string, not base64(spki(key)).