This commit adds support for EdDSA (Ed25519 and Ed448). In particular:
* It modifies prepare_tls_clienthello() to include Ed25519 and Ed448 in the signature_algorithms extension of the TLS 1.2 and earlier ClientHello (RFC 8422).
* It modifies run_server_defaults() and get_server_certificate() to check whether the server offers EdDSA certificates with TLS 1.3.
* It modifies certificate_info() to handle certificates signed with EdDSA or with EdDSA public keys, even if $OPENSSL does not support pretty printing such keys and signatures.
* It modifies read_sigalg_from_file() to recognize EdDSA signatures even if $OPENSSL does not.
Dirk Wetter
David Cooper