Tidy bssl-crypto documentation

This probably needs a few iterations, but fix the stuff I noticed on a
first pass:

- I don't think it's useful to say this is the BoringSSL implementation
  of something. That's all implicit from this crate anyway.

- Rust seems to prefer "Returns ..." rather than "Return ..."

- Algorithm names like "hkdf" or "hmac" should be written "HKDF" or
  "HMAC" when referring to the algorithms. Also BoringSSL is styled
  "BoringSSL" rather than "boringssl".

- Given Rust overall doesn't try to handle allocation failure, let's
  just write that we don't believe in allocation failure once in the
  README rather than marking which functions do and don't panic.

Change-Id: I48501717dd0b063a2fa4106c4c140d76a7ef69a9
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/60546
Reviewed-by: Nabil Wadih <nwadih@google.com>
Commit-Queue: Bob Beck <bbe@google.com>
Reviewed-by: Bob Beck <bbe@google.com>
diff --git a/rust/bssl-crypto/src/aes.rs b/rust/bssl-crypto/src/aes.rs
index e3ec5bd..e5a1607 100644
--- a/rust/bssl-crypto/src/aes.rs
+++ b/rust/bssl-crypto/src/aes.rs
@@ -23,7 +23,7 @@
 pub struct Aes;
 
 impl Aes {
-    /// Encrypt `block` in place.
+    /// Encrypts `block` in place.
     pub fn encrypt(key: &AesEncryptKey, block: &mut AesBlock) {
         let input = *block;
         // Safety:
@@ -31,7 +31,7 @@
         unsafe { bssl_sys::AES_encrypt(input.as_ptr(), block.as_mut_ptr(), &key.0) }
     }
 
-    /// Decrypt `block` in place.
+    /// Decrypts `block` in place.
     pub fn decrypt(key: &AesDecryptKey, block: &mut AesBlock) {
         let input = *block;
         // Safety: