Format descriptions in schema docs are imprecise

The schema docs stay things like:

> Pem encoded public key
> Pem encoded private key

The format is called PEM, not Pem. I guess the types do the camel-case thing on the initialisms, but docs for human consumption should use the more conventional "PEM" spelling.

> DER encoded public key

This doesn't say the format. It should specify whether this is a SubjectPublicKeyInfo or RSAPublicKey or whatever. Sampling things, it seems SubejctPublicKeyInfo is the most common, but I haven't checked all of them.

> Pkcs 8 encoded private key

I mean, this is actually specific, but in human docs, it should be styled "PKCS #8". (If we're touching it, I might say "PKCS #8 PrivateKeyInfo" since PKCS #8 is the document.)

But I also agree with https://github.com/C2SP/wycheproof/issues/178#issuecomment-3247355377 that maybe we shouldn't have so many formats.