Various documentation fixes.

Add some missing headers and ensure each header has a short description. doc.go
gets confused at declarations that break before the first (, so avoid doing
that. Also skip a/an/deprecated: in markupFirstWord and process pipe words in
the table of contents.

Change-Id: Ia08ec5ae8e496dd617e377e154eeea74f4abf435
Reviewed-on: https://boringssl-review.googlesource.com/2839
Reviewed-by: Adam Langley <agl@google.com>

include/openssl/sha.h

diff --git a/include/openssl/sha.h b/include/openssl/sha.h
index 1f321fc..5b363ee 100644
--- a/include/openssl/sha.h
+++ b/include/openssl/sha.h
@@ -64,7 +64,7 @@
 #endif
 
 
-/* SHA-1. */
+/* The SHA family of hash functions (SHA-1 and SHA-2). */
 
 
 /* SHA_CBLOCK is the block size of SHA-1. */