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/cpu.h

diff --git a/include/openssl/cpu.h b/include/openssl/cpu.h
index 5f60754..81121f1 100644
--- a/include/openssl/cpu.h
+++ b/include/openssl/cpu.h
@@ -68,6 +68,9 @@
 #endif
 
 
+/* Runtime CPU feature support */
+
+
 #if defined(OPENSSL_X86) || defined(OPENSSL_X86_64)
 /* OPENSSL_ia32cap_P contains the Intel CPUID bits when running on an x86 or
  * x86-64 system.