Spellcheck our public headers.

Also fix some formatting.

Change-Id: I8fb1a95d4a55e40127433f0114fd08a82a4c3d41
Reviewed-on: https://boringssl-review.googlesource.com/13103
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/aead.h b/include/openssl/aead.h
index eaa2b8f..35e0f13 100644
--- a/include/openssl/aead.h
+++ b/include/openssl/aead.h
@@ -64,7 +64,7 @@
  *
  * The "seal" and "open" operations are atomic - an entire message must be
  * encrypted or decrypted in a single call. Large messages may have to be split
- * up in order to accomodate this. When doing so, be mindful of the need not to
+ * up in order to accommodate this. When doing so, be mindful of the need not to
  * repeat nonces and the possibility that an attacker could duplicate, reorder
  * or drop message chunks. For example, using a single key for a given (large)
  * message and sealing chunks with nonces counting from zero would be secure as