Document extensions to FROST

Also makes misc other doc corrections.

crypto/schnorr/src/aggregate.rs

@@ -59,7 +59,7 @@ fn digest_yield<D: Digest, F: PrimeField>(digest: D, i: usize) -> F {
   ))
 }
 
-/// Aggregate Schnorr signature as defined in https://eprint.iacr.org/2021/350.pdf.
+/// Aggregate Schnorr signature as defined in https://eprint.iacr.org/2021/350.
 #[allow(non_snake_case)]
 #[derive(Clone, PartialEq, Eq, Debug, Zeroize)]
 pub struct SchnorrAggregate<C: Ciphersuite> {

crypto/transcript/src/lib.rs

@@ -98,5 +98,6 @@ impl<D: Clone + SecureDigest> Transcript for DigestTranscript<D> {
   }
 }
 
+/// The recommended transcript, secure against length-extension attacks.
 #[cfg(feature = "recommended")]
 pub type RecommendedTranscript = DigestTranscript<blake2::Blake2b512>;