Before, things worked like this:
* Only signatures of Ed25519 keys could be verified
* Key encoding placed the plain binary Ed25519 key in the PEM, instead of the
key's ASN1 encoding
With this patch it now works like this:
* Ed25519 signatures are supported as before
* RSA keys are now supported too, assuming RSA-SHA256 signatures
* Both Ed25519 and RSA keys are encoded and decoded using actual PEM with ASN1
