Improve DocC landing pages (#313)

Improve DocC landing pages by mimicking Apple's CryptoKit docs

### Motivation:

Right now the DocC docs group all APIs by protocols, structures and
enums.
By adding a topics section in the landing page we can group them by type
("Ciphers", "Public key cryptography", etc.) exactly in the way Apple
does in [CryptoKit
docs](https://developer.apple.com/documentation/cryptokit/).

### Modifications:

- Fix DocC compilation errors in `_CryptoExtras`
- Add topics section in `_CryptoExtras` landing page
- Add topics section in `Crypto` landing page

### Result:

APIs will be grouped by type.

---------

Co-authored-by: Cory Benfield <[email protected]>

Sources/Crypto/Docs.docc/index.md

@@ -9,4 +9,46 @@ Swift Crypto provides a Swift library for common cryptographic operations. It is
 * `Crypto` - an open-source implementation of a substantial portion of the API of [Apple CryptoKit](https://developer.apple.com/documentation/cryptokit) suitable for use on Linux platforms. It enables cross-platform or server applications with the advantages of CryptoKit.
 * `CryptoExtras` - a collection of additional cryptographic primitives and utilities that are not part of CryptoKit but useful in a server environment.
 
-Swift Crypto is built on top of [BoringSSL](https://boringssl.googlesource.com/boringssl/), Google's fork of OpenSSL. The current features of Swift Crypto cover key exchange, key derivation, encryption and decryption, hashing, message authentication, and more.
+Swift Crypto is built on top of [BoringSSL](https://boringssl.googlesource.com/boringssl/), Google's fork of OpenSSL. The current features of Swift Crypto cover key exchange, key derivation, encryption and decryption, hashing, message authentication, and more.
+
+## Topics
+
+### Cryptographically secure hashes
+
+- ``HashFunction``
+- ``SHA512``
+- ``SHA384``
+- ``SHA256``
+
+### Message authentication codes
+
+- ``HMAC``
+- ``SymmetricKey``
+- ``SymmetricKeySize``
+
+### Ciphers
+
+- ``AES``
+- ``ChaChaPoly``
+
+### Public key cryptography
+
+- ``Curve25519``
+- ``P521``
+- ``P384``
+- ``P256``
+- ``SharedSecret``
+- ``HPKE``
+
+### Key derivation functions
+
+- ``HKDF``
+
+### Errors
+
+- ``CryptoKitError``
+- ``CryptoKitASN1Error``
+
+### Legacy algorithms
+
+- ``Insecure``

Sources/_CryptoExtras/Docs.docc/index.md

@@ -2,4 +2,24 @@
 
 Provides additional cryptographic APIs that are not available in CryptoKit (and therefore the core Crypto library).
 
+## Overview
 
+`CryptoExtras` is a collection of additional cryptographic primitives and utilities that are not part of CryptoKit but useful in a server environment.
+
+## Topics
+
+### Ciphers
+
+- ``_CryptoExtras/Crypto/AES``
+
+### Public key cryptography
+
+- ``_RSA``
+
+### Key derivation functions
+
+- ``KDF``
+
+### Legacy algorithms
+
+- ``_CryptoExtras/Crypto/Insecure``

Sources/_CryptoExtras/RSA/RSA+BlindSigning.swift

@@ -410,7 +410,7 @@ extension _RSA.BlindSigning.PublicKey {
     /// Prepare a message to be signed using the blind signing protocol.
     ///
     /// - Parameter message: The message to be signed.
-    /// - Parameter parameters: Parameters used in the blind signing protocol.
+    ///
     /// - Returns: A prepared message, modified according to the parameters provided.
     ///
     /// - Seealso: [RFC 9474: Prepare](https://www.rfc-editor.org/rfc/rfc9474.html#name-prepare).
@@ -440,7 +440,7 @@ extension _RSA.BlindSigning.PublicKey {
     ///
     /// - Parameter signature: The signature of the blinded message.
     /// - Parameter message: The message to be signed.
-    /// - Parameter blindInverse: The inverse from the message blinding.
+    /// - Parameter blindingInverse: The inverse from the message blinding.
     /// - Returns: The signature of the message.
     ///
     /// - Seealso: [RFC 9474: Finalize](https://www.rfc-editor.org/rfc/rfc9474.html#name-finalize).